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mox!
This commit is contained in:
849
dkim/dkim.go
Normal file
849
dkim/dkim.go
Normal file
@ -0,0 +1,849 @@
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// Package dkim (DomainKeys Identified Mail signatures, RFC 6376) signs and
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// verifies DKIM signatures.
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//
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// Signatures are added to email messages in DKIM-Signature headers. By signing a
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// message, a domain takes responsibility for the message. A message can have
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// signatures for multiple domains, and the domain does not necessarily have to
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// match a domain in a From header. Receiving mail servers can build a spaminess
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// reputation based on domains that signed the message, along with other
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// mechanisms.
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package dkim
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import (
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"bufio"
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"bytes"
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"context"
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"crypto"
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"crypto/ed25519"
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cryptorand "crypto/rand"
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"crypto/rsa"
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"errors"
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"fmt"
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"hash"
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"io"
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"strings"
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"time"
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"github.com/prometheus/client_golang/prometheus"
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"github.com/prometheus/client_golang/prometheus/promauto"
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"github.com/mjl-/mox/config"
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"github.com/mjl-/mox/dns"
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"github.com/mjl-/mox/mlog"
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"github.com/mjl-/mox/moxio"
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"github.com/mjl-/mox/publicsuffix"
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"github.com/mjl-/mox/smtp"
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)
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var xlog = mlog.New("dkim")
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var (
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metricDKIMSign = promauto.NewCounterVec(
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prometheus.CounterOpts{
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Name: "mox_dkim_sign_total",
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Help: "DKIM messages signings.",
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},
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[]string{
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"key",
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},
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)
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metricDKIMVerify = promauto.NewHistogramVec(
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prometheus.HistogramOpts{
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Name: "mox_dkim_verify_duration_seconds",
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Help: "DKIM verify, including lookup, duration and result.",
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Buckets: []float64{0.001, 0.005, 0.01, 0.05, 0.100, 0.5, 1, 5, 10, 20},
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},
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[]string{
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"algorithm",
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"status",
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},
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)
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)
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var timeNow = time.Now // Replaced during tests.
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// Status is the result of verifying a DKIM-Signature as described by RFC 8601,
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// "Message Header Field for Indicating Message Authentication Status".
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type Status string
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// ../rfc/8601:959 ../rfc/6376:1770 ../rfc/6376:2459
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const (
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StatusNone Status = "none" // Message was not signed.
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StatusPass Status = "pass" // Message was signed and signature was verified.
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StatusFail Status = "fail" // Message was signed, but signature was invalid.
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StatusPolicy Status = "policy" // Message was signed, but signature is not accepted by policy.
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StatusNeutral Status = "neutral" // Message was signed, but the signature contains an error or could not be processed. This status is also used for errors not covered by other statuses.
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StatusTemperror Status = "temperror" // Message could not be verified. E.g. because of DNS resolve error. A later attempt may succeed. A missing DNS record is treated as temporary error, a new key may not have propagated through DNS shortly after it was taken into use.
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StatusPermerror Status = "permerror" // Message cannot be verified. E.g. when a required header field is absent or for invalid (combination of) parameters. Typically set if a DNS record does not allow the signature, e.g. due to algorithm mismatch or expiry.
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)
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// Lookup errors.
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var (
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ErrNoRecord = errors.New("dkim: no dkim dns record for selector and domain")
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ErrMultipleRecords = errors.New("dkim: multiple dkim dns record for selector and domain")
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ErrDNS = errors.New("dkim: lookup of dkim dns record")
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ErrSyntax = errors.New("dkim: syntax error in dkim dns record")
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)
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// Signature verification errors.
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var (
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ErrSigAlgMismatch = errors.New("dkim: signature algorithm mismatch with dns record")
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ErrHashAlgNotAllowed = errors.New("dkim: hash algorithm not allowed by dns record")
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ErrKeyNotForEmail = errors.New("dkim: dns record not allowed for use with email")
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ErrDomainIdentityMismatch = errors.New("dkim: dns record disallows mismatch of domain (d=) and identity (i=)")
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ErrSigExpired = errors.New("dkim: signature has expired")
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ErrHashAlgorithmUnknown = errors.New("dkim: unknown hash algorithm")
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ErrBodyhashMismatch = errors.New("dkim: body hash does not match")
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ErrSigVerify = errors.New("dkim: signature verification failed")
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ErrSigAlgorithmUnknown = errors.New("dkim: unknown signature algorithm")
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ErrCanonicalizationUnknown = errors.New("dkim: unknown canonicalization")
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ErrHeaderMalformed = errors.New("dkim: mail message header is malformed")
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ErrFrom = errors.New("dkim: bad from headers")
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ErrQueryMethod = errors.New("dkim: no recognized query method")
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ErrKeyRevoked = errors.New("dkim: key has been revoked")
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ErrTLD = errors.New("dkim: signed domain is top-level domain, above organizational domain")
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ErrPolicy = errors.New("dkim: signature rejected by policy")
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ErrWeakKey = errors.New("dkim: key is too weak, need at least 1024 bits for rsa")
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)
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// Result is the conclusion of verifying one DKIM-Signature header. An email can
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// have multiple signatures, each with different parameters.
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//
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// To decide what to do with a message, both the signature parameters and the DNS
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// TXT record have to be consulted.
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type Result struct {
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Status Status
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Sig *Sig // Parsed form of DKIM-Signature header. Can be nil for invalid DKIM-Signature header.
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Record *Record // Parsed form of DKIM DNS record for selector and domain in Sig. Optional.
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Err error // If Status is not StatusPass, this error holds the details and can be checked using errors.Is.
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}
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// todo: use some io.Writer to hash the body and the header.
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// Sign returns line(s) with DKIM-Signature headers, generated according to the configuration.
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func Sign(ctx context.Context, localpart smtp.Localpart, domain dns.Domain, c config.DKIM, smtputf8 bool, msg io.ReaderAt) (headers string, rerr error) {
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log := xlog.WithContext(ctx)
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start := timeNow()
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defer func() {
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log.Debugx("dkim sign result", rerr, mlog.Field("localpart", localpart), mlog.Field("domain", domain), mlog.Field("smtputf8", smtputf8), mlog.Field("duration", time.Since(start)))
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}()
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hdrs, bodyOffset, err := parseHeaders(bufio.NewReader(&moxio.AtReader{R: msg}))
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if err != nil {
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return "", fmt.Errorf("%w: %s", ErrHeaderMalformed, err)
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}
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nfrom := 0
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for _, h := range hdrs {
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if h.lkey == "from" {
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nfrom++
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}
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}
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if nfrom != 1 {
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return "", fmt.Errorf("%w: message has %d from headers, need exactly 1", ErrFrom, nfrom)
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}
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type hashKey struct {
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simple bool // Canonicalization.
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hash string // lower-case hash.
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}
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var bodyHashes = map[hashKey][]byte{}
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for _, sign := range c.Sign {
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sel := c.Selectors[sign]
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sig := newSigWithDefaults()
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sig.Version = 1
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switch sel.Key.(type) {
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case *rsa.PrivateKey:
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sig.AlgorithmSign = "rsa"
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metricDKIMSign.WithLabelValues("rsa").Inc()
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case ed25519.PrivateKey:
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sig.AlgorithmSign = "ed25519"
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metricDKIMSign.WithLabelValues("ed25519").Inc()
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default:
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return "", fmt.Errorf("internal error, unknown pivate key %T", sel.Key)
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}
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sig.AlgorithmHash = sel.HashEffective
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sig.Domain = domain
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sig.Selector = sel.Domain
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sig.Identity = &Identity{&localpart, domain}
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sig.SignedHeaders = append([]string{}, sel.HeadersEffective...)
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if !sel.DontSealHeaders {
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// ../rfc/6376:2156
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// Each time a header name is added to the signature, the next unused value is
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// signed (in reverse order as they occur in the message). So we can add each
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// header name as often as it occurs. But now we'll add the header names one
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// additional time, preventing someone from adding one more header later on.
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counts := map[string]int{}
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for _, h := range hdrs {
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counts[h.lkey]++
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}
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for _, h := range sel.HeadersEffective {
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for j := counts[strings.ToLower(h)]; j > 0; j-- {
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sig.SignedHeaders = append(sig.SignedHeaders, h)
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}
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}
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}
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sig.SignTime = timeNow().Unix()
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if sel.ExpirationSeconds > 0 {
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sig.ExpireTime = sig.SignTime + int64(sel.ExpirationSeconds)
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}
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sig.Canonicalization = "simple"
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if sel.Canonicalization.HeaderRelaxed {
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sig.Canonicalization = "relaxed"
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}
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sig.Canonicalization += "/"
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if sel.Canonicalization.BodyRelaxed {
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sig.Canonicalization += "relaxed"
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} else {
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sig.Canonicalization += "simple"
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}
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h, hok := algHash(sig.AlgorithmHash)
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if !hok {
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return "", fmt.Errorf("unrecognized hash algorithm %q", sig.AlgorithmHash)
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}
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// We must now first calculate the hash over the body. Then include that hash in a
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// new DKIM-Signature header. Then hash that and the signed headers into a data
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// hash. Then that hash is finally signed and the signature included in the new
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// DKIM-Signature header.
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// ../rfc/6376:1700
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hk := hashKey{!sel.Canonicalization.BodyRelaxed, strings.ToLower(sig.AlgorithmHash)}
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if bh, ok := bodyHashes[hk]; ok {
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sig.BodyHash = bh
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} else {
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br := bufio.NewReader(&moxio.AtReader{R: msg, Offset: int64(bodyOffset)})
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bh, err = bodyHash(h.New(), !sel.Canonicalization.BodyRelaxed, br)
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if err != nil {
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return "", err
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}
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sig.BodyHash = bh
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bodyHashes[hk] = bh
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}
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sigh, err := sig.Header()
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if err != nil {
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return "", err
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}
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verifySig := []byte(strings.TrimSuffix(sigh, "\r\n"))
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dh, err := dataHash(h.New(), !sel.Canonicalization.HeaderRelaxed, sig, hdrs, verifySig)
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if err != nil {
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return "", err
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}
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switch key := sel.Key.(type) {
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case *rsa.PrivateKey:
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sig.Signature, err = key.Sign(cryptorand.Reader, dh, h)
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if err != nil {
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return "", fmt.Errorf("signing data: %v", err)
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}
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case ed25519.PrivateKey:
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// crypto.Hash(0) indicates data isn't prehashed (ed25519ph). We are using
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// PureEdDSA to sign the sha256 hash. ../rfc/8463:123 ../rfc/8032:427
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sig.Signature, err = key.Sign(cryptorand.Reader, dh, crypto.Hash(0))
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if err != nil {
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return "", fmt.Errorf("signing data: %v", err)
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}
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default:
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return "", fmt.Errorf("unsupported private key type: %s", err)
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}
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sigh, err = sig.Header()
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if err != nil {
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return "", err
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}
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headers += sigh
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}
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return headers, nil
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}
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// Lookup looks up the DKIM TXT record and parses it.
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//
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// A requested record is <selector>._domainkey.<domain>. Exactly one valid DKIM
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// record should be present.
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func Lookup(ctx context.Context, resolver dns.Resolver, selector, domain dns.Domain) (rstatus Status, rrecord *Record, rtxt string, rerr error) {
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log := xlog.WithContext(ctx)
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start := timeNow()
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defer func() {
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log.Debugx("dkim lookup result", rerr, mlog.Field("selector", selector), mlog.Field("domain", domain), mlog.Field("status", rstatus), mlog.Field("record", rrecord), mlog.Field("duration", time.Since(start)))
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}()
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name := selector.ASCII + "._domainkey." + domain.ASCII + "."
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records, err := dns.WithPackage(resolver, "dkim").LookupTXT(ctx, name)
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if dns.IsNotFound(err) {
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// ../rfc/6376:2608
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// We must return StatusPermerror. We may want to return StatusTemperror because in
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// practice someone will start using a new key before DNS changes have propagated.
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return StatusPermerror, nil, "", fmt.Errorf("%w: dns name %q", ErrNoRecord, name)
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} else if err != nil {
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return StatusTemperror, nil, "", fmt.Errorf("%w: dns name %q: %s", ErrDNS, name, err)
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}
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// ../rfc/6376:2612
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var status = StatusTemperror
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var record *Record
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var txt string
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err = nil
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for _, s := range records {
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// We interpret ../rfc/6376:2621 to mean that a record that claims to be v=DKIM1,
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// but isn't actually valid, results in a StatusPermFail. But a record that isn't
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// claiming to be DKIM1 is ignored.
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var r *Record
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var isdkim bool
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r, isdkim, err = ParseRecord(s)
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if err != nil && isdkim {
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return StatusPermerror, nil, txt, fmt.Errorf("%w: %s", ErrSyntax, err)
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} else if err != nil {
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// Hopefully the remote MTA admin discovers the configuration error and fix it for
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// an upcoming delivery attempt, in case we rejected with temporary status.
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status = StatusTemperror
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err = fmt.Errorf("%w: not a dkim record: %s", ErrSyntax, err)
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continue
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}
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// If there are multiple valid records, return a temporary error. Perhaps the error is fixed soon.
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// ../rfc/6376:1609
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// ../rfc/6376:2584
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if record != nil {
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return StatusTemperror, nil, "", fmt.Errorf("%w: dns name %q", ErrMultipleRecords, name)
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}
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record = r
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txt = s
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err = nil
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}
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if record == nil {
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return status, nil, "", err
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}
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return StatusNeutral, record, txt, nil
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}
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// Verify parses the DKIM-Signature headers in a message and verifies each of them.
|
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//
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// If the headers of the message cannot be found, an error is returned.
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// Otherwise, each DKIM-Signature header is reflected in the returned results.
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//
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// NOTE: Verify does not check if the domain (d=) that signed the message is
|
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// the domain of the sender. The caller, e.g. through DMARC, should do this.
|
||||
//
|
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// If ignoreTestMode is true and the DKIM record is in test mode (t=y), a
|
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// verification failure is treated as actual failure. With ignoreTestMode
|
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// false, such verification failures are treated as if there is no signature by
|
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// returning StatusNone.
|
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func Verify(ctx context.Context, resolver dns.Resolver, smtputf8 bool, policy func(*Sig) error, r io.ReaderAt, ignoreTestMode bool) (results []Result, rerr error) {
|
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log := xlog.WithContext(ctx)
|
||||
start := timeNow()
|
||||
defer func() {
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duration := float64(time.Since(start)) / float64(time.Second)
|
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for _, r := range results {
|
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var alg string
|
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if r.Sig != nil {
|
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alg = r.Sig.Algorithm()
|
||||
}
|
||||
status := string(r.Status)
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metricDKIMVerify.WithLabelValues(alg, status).Observe(duration)
|
||||
}
|
||||
|
||||
if len(results) == 0 {
|
||||
log.Debugx("dkim verify result", rerr, mlog.Field("smtputf8", smtputf8), mlog.Field("duration", time.Since(start)))
|
||||
}
|
||||
for _, result := range results {
|
||||
log.Debugx("dkim verify result", result.Err, mlog.Field("smtputf8", smtputf8), mlog.Field("status", result.Status), mlog.Field("sig", result.Sig), mlog.Field("record", result.Record), mlog.Field("duration", time.Since(start)))
|
||||
}
|
||||
}()
|
||||
|
||||
hdrs, bodyOffset, err := parseHeaders(bufio.NewReader(&moxio.AtReader{R: r}))
|
||||
if err != nil {
|
||||
return nil, fmt.Errorf("%w: %s", ErrHeaderMalformed, err)
|
||||
}
|
||||
|
||||
// todo: reuse body hashes and possibly verify signatures in parallel. and start the dns lookup immediately. ../rfc/6376:2697
|
||||
|
||||
for _, h := range hdrs {
|
||||
if h.lkey != "dkim-signature" {
|
||||
continue
|
||||
}
|
||||
|
||||
sig, verifySig, err := parseSignature(h.raw, smtputf8)
|
||||
if err != nil {
|
||||
// ../rfc/6376:2503
|
||||
err := fmt.Errorf("parsing DKIM-Signature header: %w", err)
|
||||
results = append(results, Result{StatusPermerror, nil, nil, err})
|
||||
continue
|
||||
}
|
||||
|
||||
h, canonHeaderSimple, canonDataSimple, err := checkSignatureParams(ctx, sig)
|
||||
if err != nil {
|
||||
results = append(results, Result{StatusPermerror, nil, nil, err})
|
||||
continue
|
||||
}
|
||||
|
||||
// ../rfc/6376:2560
|
||||
if err := policy(sig); err != nil {
|
||||
err := fmt.Errorf("%w: %s", ErrPolicy, err)
|
||||
results = append(results, Result{StatusPolicy, nil, nil, err})
|
||||
continue
|
||||
}
|
||||
|
||||
br := bufio.NewReader(&moxio.AtReader{R: r, Offset: int64(bodyOffset)})
|
||||
status, txt, err := verifySignature(ctx, resolver, sig, h, canonHeaderSimple, canonDataSimple, hdrs, verifySig, br, ignoreTestMode)
|
||||
results = append(results, Result{status, sig, txt, err})
|
||||
}
|
||||
return results, nil
|
||||
}
|
||||
|
||||
// check if signature is acceptable.
|
||||
// Only looks at the signature parameters, not at the DNS record.
|
||||
func checkSignatureParams(ctx context.Context, sig *Sig) (hash crypto.Hash, canonHeaderSimple, canonBodySimple bool, rerr error) {
|
||||
// "From" header is required, ../rfc/6376:2122 ../rfc/6376:2546
|
||||
var from bool
|
||||
for _, h := range sig.SignedHeaders {
|
||||
if strings.EqualFold(h, "from") {
|
||||
from = true
|
||||
break
|
||||
}
|
||||
}
|
||||
if !from {
|
||||
return 0, false, false, fmt.Errorf(`%w: required "from" header not signed`, ErrFrom)
|
||||
}
|
||||
|
||||
// ../rfc/6376:2550
|
||||
if sig.ExpireTime >= 0 && sig.ExpireTime < timeNow().Unix() {
|
||||
return 0, false, false, fmt.Errorf("%w: expiration time %q", ErrSigExpired, time.Unix(sig.ExpireTime, 0).Format(time.RFC3339))
|
||||
}
|
||||
|
||||
// ../rfc/6376:2554
|
||||
// ../rfc/6376:3284
|
||||
// Refuse signatures that reach beyond declared scope. We use the existing
|
||||
// publicsuffix.Lookup to lookup a fake subdomain of the signing domain. If this
|
||||
// supposed subdomain is actually an organizational domain, the signing domain
|
||||
// shouldn't be signing for its organizational domain.
|
||||
subdom := sig.Domain
|
||||
subdom.ASCII = "x." + subdom.ASCII
|
||||
if subdom.Unicode != "" {
|
||||
subdom.Unicode = "x." + subdom.Unicode
|
||||
}
|
||||
if orgDom := publicsuffix.Lookup(ctx, subdom); subdom.ASCII == orgDom.ASCII {
|
||||
return 0, false, false, fmt.Errorf("%w: %s", ErrTLD, sig.Domain)
|
||||
}
|
||||
|
||||
h, hok := algHash(sig.AlgorithmHash)
|
||||
if !hok {
|
||||
return 0, false, false, fmt.Errorf("%w: %q", ErrHashAlgorithmUnknown, sig.AlgorithmHash)
|
||||
}
|
||||
|
||||
t := strings.SplitN(sig.Canonicalization, "/", 2)
|
||||
|
||||
switch strings.ToLower(t[0]) {
|
||||
case "simple":
|
||||
canonHeaderSimple = true
|
||||
case "relaxed":
|
||||
default:
|
||||
return 0, false, false, fmt.Errorf("%w: header canonicalization %q", ErrCanonicalizationUnknown, sig.Canonicalization)
|
||||
}
|
||||
|
||||
canon := "simple"
|
||||
if len(t) == 2 {
|
||||
canon = t[1]
|
||||
}
|
||||
switch strings.ToLower(canon) {
|
||||
case "simple":
|
||||
canonBodySimple = true
|
||||
case "relaxed":
|
||||
default:
|
||||
return 0, false, false, fmt.Errorf("%w: body canonicalization %q", ErrCanonicalizationUnknown, sig.Canonicalization)
|
||||
}
|
||||
|
||||
// We only recognize query method dns/txt, which is the default. ../rfc/6376:1268
|
||||
if len(sig.QueryMethods) > 0 {
|
||||
var dnstxt bool
|
||||
for _, m := range sig.QueryMethods {
|
||||
if strings.EqualFold(m, "dns/txt") {
|
||||
dnstxt = true
|
||||
break
|
||||
}
|
||||
}
|
||||
if !dnstxt {
|
||||
return 0, false, false, fmt.Errorf("%w: need dns/txt", ErrQueryMethod)
|
||||
}
|
||||
}
|
||||
|
||||
return h, canonHeaderSimple, canonBodySimple, nil
|
||||
}
|
||||
|
||||
// lookup the public key in the DNS and verify the signature.
|
||||
func verifySignature(ctx context.Context, resolver dns.Resolver, sig *Sig, hash crypto.Hash, canonHeaderSimple, canonDataSimple bool, hdrs []header, verifySig []byte, body *bufio.Reader, ignoreTestMode bool) (Status, *Record, error) {
|
||||
// ../rfc/6376:2604
|
||||
status, record, _, err := Lookup(ctx, resolver, sig.Selector, sig.Domain)
|
||||
if err != nil {
|
||||
// todo: for temporary errors, we could pass on information so caller returns a 4.7.5 ecode, ../rfc/6376:2777
|
||||
return status, nil, err
|
||||
}
|
||||
status, err = verifySignatureRecord(record, sig, hash, canonHeaderSimple, canonDataSimple, hdrs, verifySig, body, ignoreTestMode)
|
||||
return status, record, err
|
||||
}
|
||||
|
||||
// verify a DKIM signature given the record from dns and signature from the email message.
|
||||
func verifySignatureRecord(r *Record, sig *Sig, hash crypto.Hash, canonHeaderSimple, canonDataSimple bool, hdrs []header, verifySig []byte, body *bufio.Reader, ignoreTestMode bool) (rstatus Status, rerr error) {
|
||||
if !ignoreTestMode {
|
||||
// ../rfc/6376:1558
|
||||
y := false
|
||||
for _, f := range r.Flags {
|
||||
if strings.EqualFold(f, "y") {
|
||||
y = true
|
||||
break
|
||||
}
|
||||
}
|
||||
if y {
|
||||
defer func() {
|
||||
if rstatus != StatusPass {
|
||||
rstatus = StatusNone
|
||||
}
|
||||
}()
|
||||
}
|
||||
}
|
||||
|
||||
// ../rfc/6376:2639
|
||||
if len(r.Hashes) > 0 {
|
||||
ok := false
|
||||
for _, h := range r.Hashes {
|
||||
if strings.EqualFold(h, sig.AlgorithmHash) {
|
||||
ok = true
|
||||
break
|
||||
}
|
||||
}
|
||||
if !ok {
|
||||
return StatusPermerror, fmt.Errorf("%w: dkim dns record expects one of %q, message uses %q", ErrHashAlgNotAllowed, strings.Join(r.Hashes, ","), sig.AlgorithmHash)
|
||||
}
|
||||
}
|
||||
|
||||
// ../rfc/6376:2651
|
||||
if !strings.EqualFold(r.Key, sig.AlgorithmSign) {
|
||||
return StatusPermerror, fmt.Errorf("%w: dkim dns record requires algorithm %q, message has %q", ErrSigAlgMismatch, r.Key, sig.AlgorithmSign)
|
||||
}
|
||||
|
||||
// ../rfc/6376:2645
|
||||
if r.PublicKey == nil {
|
||||
return StatusPermerror, ErrKeyRevoked
|
||||
} else if rsaKey, ok := r.PublicKey.(*rsa.PublicKey); ok && rsaKey.N.BitLen() < 1024 {
|
||||
// todo: find a reference that supports this.
|
||||
return StatusPermerror, ErrWeakKey
|
||||
}
|
||||
|
||||
// ../rfc/6376:1541
|
||||
if !r.ServiceAllowed("email") {
|
||||
return StatusPermerror, ErrKeyNotForEmail
|
||||
}
|
||||
for _, t := range r.Flags {
|
||||
// ../rfc/6376:1575
|
||||
// ../rfc/6376:1805
|
||||
if strings.EqualFold(t, "s") && sig.Identity != nil {
|
||||
if sig.Identity.Domain.ASCII != sig.Domain.ASCII {
|
||||
return StatusPermerror, fmt.Errorf("%w: i= identity domain %q must match d= domain %q", ErrDomainIdentityMismatch, sig.Domain.ASCII, sig.Identity.Domain.ASCII)
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
if sig.Length >= 0 {
|
||||
// todo future: implement l= parameter in signatures. we don't currently allow this through policy check.
|
||||
return StatusPermerror, fmt.Errorf("l= (length) parameter in signature not yet implemented")
|
||||
}
|
||||
|
||||
// We first check the signature is with the claimed body hash is valid. Then we
|
||||
// verify the body hash. In case of invalid signatures, we won't read the entire
|
||||
// body.
|
||||
// ../rfc/6376:1700
|
||||
// ../rfc/6376:2656
|
||||
|
||||
dh, err := dataHash(hash.New(), canonHeaderSimple, sig, hdrs, verifySig)
|
||||
if err != nil {
|
||||
// Any error is likely an invalid header field in the message, hence permanent error.
|
||||
return StatusPermerror, fmt.Errorf("calculating data hash: %w", err)
|
||||
}
|
||||
|
||||
switch k := r.PublicKey.(type) {
|
||||
case *rsa.PublicKey:
|
||||
if err := rsa.VerifyPKCS1v15(k, hash, dh, sig.Signature); err != nil {
|
||||
return StatusFail, fmt.Errorf("%w: rsa verification: %s", ErrSigVerify, err)
|
||||
}
|
||||
case ed25519.PublicKey:
|
||||
if ok := ed25519.Verify(k, dh, sig.Signature); !ok {
|
||||
return StatusFail, fmt.Errorf("%w: ed25519 verification", ErrSigVerify)
|
||||
}
|
||||
default:
|
||||
return StatusPermerror, fmt.Errorf("%w: unrecognized signature algorithm %q", ErrSigAlgorithmUnknown, r.Key)
|
||||
}
|
||||
|
||||
bh, err := bodyHash(hash.New(), canonDataSimple, body)
|
||||
if err != nil {
|
||||
// Any error is likely some internal error, hence temporary error.
|
||||
return StatusTemperror, fmt.Errorf("calculating body hash: %w", err)
|
||||
}
|
||||
if !bytes.Equal(sig.BodyHash, bh) {
|
||||
return StatusFail, fmt.Errorf("%w: signature bodyhash %x != calculated bodyhash %x", ErrBodyhashMismatch, sig.BodyHash, bh)
|
||||
}
|
||||
|
||||
return StatusPass, nil
|
||||
}
|
||||
|
||||
func algHash(s string) (crypto.Hash, bool) {
|
||||
if strings.EqualFold(s, "sha1") {
|
||||
return crypto.SHA1, true
|
||||
} else if strings.EqualFold(s, "sha256") {
|
||||
return crypto.SHA256, true
|
||||
}
|
||||
return 0, false
|
||||
}
|
||||
|
||||
// bodyHash calculates the hash over the body.
|
||||
func bodyHash(h hash.Hash, canonSimple bool, body *bufio.Reader) ([]byte, error) {
|
||||
// todo: take l= into account. we don't currently allow it for policy reasons.
|
||||
|
||||
var crlf = []byte("\r\n")
|
||||
|
||||
if canonSimple {
|
||||
// ../rfc/6376:864, ensure body ends with exactly one trailing crlf.
|
||||
ncrlf := 0
|
||||
for {
|
||||
buf, err := body.ReadBytes('\n')
|
||||
if len(buf) == 0 && err == io.EOF {
|
||||
break
|
||||
}
|
||||
if err != nil && err != io.EOF {
|
||||
return nil, err
|
||||
}
|
||||
hascrlf := bytes.HasSuffix(buf, crlf)
|
||||
if hascrlf {
|
||||
buf = buf[:len(buf)-2]
|
||||
}
|
||||
if len(buf) > 0 {
|
||||
for ; ncrlf > 0; ncrlf-- {
|
||||
h.Write(crlf)
|
||||
}
|
||||
h.Write(buf)
|
||||
}
|
||||
if hascrlf {
|
||||
ncrlf++
|
||||
}
|
||||
}
|
||||
h.Write(crlf)
|
||||
} else {
|
||||
hb := bufio.NewWriter(h)
|
||||
|
||||
// We go through the body line by line, replacing WSP with a single space and removing whitespace at the end of lines.
|
||||
// We stash "empty" lines. If they turn out to be at the end of the file, we must drop them.
|
||||
stash := &bytes.Buffer{}
|
||||
var line bool // Whether buffer read is for continuation of line.
|
||||
var prev byte // Previous byte read for line.
|
||||
linesEmpty := true // Whether stash contains only empty lines and may need to be dropped.
|
||||
var bodynonempty bool // Whether body is non-empty, for adding missing crlf.
|
||||
var hascrlf bool // Whether current/last line ends with crlf, for adding missing crlf.
|
||||
for {
|
||||
// todo: should not read line at a time, count empty lines. reduces max memory usage. a message with lots of empty lines can cause high memory use.
|
||||
buf, err := body.ReadBytes('\n')
|
||||
if len(buf) == 0 && err == io.EOF {
|
||||
break
|
||||
}
|
||||
if err != nil && err != io.EOF {
|
||||
return nil, err
|
||||
}
|
||||
bodynonempty = true
|
||||
|
||||
hascrlf = bytes.HasSuffix(buf, crlf)
|
||||
if hascrlf {
|
||||
buf = buf[:len(buf)-2]
|
||||
|
||||
// ../rfc/6376:893, "ignore all whitespace at the end of lines".
|
||||
// todo: what is "whitespace"? it isn't WSP (space and tab), the next line mentions WSP explicitly for another rule. should we drop trailing \r, \n, \v, more?
|
||||
buf = bytes.TrimRight(buf, " \t")
|
||||
}
|
||||
|
||||
// Replace one or more WSP to a single SP.
|
||||
for i, c := range buf {
|
||||
wsp := c == ' ' || c == '\t'
|
||||
if (i >= 0 || line) && wsp {
|
||||
if prev == ' ' {
|
||||
continue
|
||||
}
|
||||
prev = ' '
|
||||
c = ' '
|
||||
} else {
|
||||
prev = c
|
||||
}
|
||||
if !wsp {
|
||||
linesEmpty = false
|
||||
}
|
||||
stash.WriteByte(c)
|
||||
}
|
||||
if hascrlf {
|
||||
stash.Write(crlf)
|
||||
}
|
||||
line = !hascrlf
|
||||
if !linesEmpty {
|
||||
hb.Write(stash.Bytes())
|
||||
stash.Reset()
|
||||
linesEmpty = true
|
||||
}
|
||||
}
|
||||
// ../rfc/6376:886
|
||||
// Only for non-empty bodies without trailing crlf do we add the missing crlf.
|
||||
if bodynonempty && !hascrlf {
|
||||
hb.Write(crlf)
|
||||
}
|
||||
|
||||
hb.Flush()
|
||||
}
|
||||
return h.Sum(nil), nil
|
||||
}
|
||||
|
||||
func dataHash(h hash.Hash, canonSimple bool, sig *Sig, hdrs []header, verifySig []byte) ([]byte, error) {
|
||||
headers := ""
|
||||
revHdrs := map[string][]header{}
|
||||
for _, h := range hdrs {
|
||||
revHdrs[h.lkey] = append([]header{h}, revHdrs[h.lkey]...)
|
||||
}
|
||||
|
||||
for _, key := range sig.SignedHeaders {
|
||||
lkey := strings.ToLower(key)
|
||||
h := revHdrs[lkey]
|
||||
if len(h) == 0 {
|
||||
continue
|
||||
}
|
||||
revHdrs[lkey] = h[1:]
|
||||
s := string(h[0].raw)
|
||||
if canonSimple {
|
||||
// ../rfc/6376:823
|
||||
// Add unmodified.
|
||||
headers += s
|
||||
} else {
|
||||
ch, err := relaxedCanonicalHeaderWithoutCRLF(s)
|
||||
if err != nil {
|
||||
return nil, fmt.Errorf("canonicalizing header: %w", err)
|
||||
}
|
||||
headers += ch + "\r\n"
|
||||
}
|
||||
}
|
||||
// ../rfc/6376:2377, canonicalization does not apply to the dkim-signature header.
|
||||
h.Write([]byte(headers))
|
||||
dkimSig := verifySig
|
||||
if !canonSimple {
|
||||
ch, err := relaxedCanonicalHeaderWithoutCRLF(string(verifySig))
|
||||
if err != nil {
|
||||
return nil, fmt.Errorf("canonicalizing DKIM-Signature header: %w", err)
|
||||
}
|
||||
dkimSig = []byte(ch)
|
||||
}
|
||||
h.Write(dkimSig)
|
||||
return h.Sum(nil), nil
|
||||
}
|
||||
|
||||
// a single header, can be multiline.
|
||||
func relaxedCanonicalHeaderWithoutCRLF(s string) (string, error) {
|
||||
// ../rfc/6376:831
|
||||
t := strings.SplitN(s, ":", 2)
|
||||
if len(t) != 2 {
|
||||
return "", fmt.Errorf("%w: invalid header %q", ErrHeaderMalformed, s)
|
||||
}
|
||||
|
||||
// Unfold, we keep the leading WSP on continuation lines and fix it up below.
|
||||
v := strings.ReplaceAll(t[1], "\r\n", "")
|
||||
|
||||
// Replace one or more WSP to a single SP.
|
||||
var nv []byte
|
||||
var prev byte
|
||||
for i, c := range []byte(v) {
|
||||
if i >= 0 && c == ' ' || c == '\t' {
|
||||
if prev == ' ' {
|
||||
continue
|
||||
}
|
||||
prev = ' '
|
||||
c = ' '
|
||||
} else {
|
||||
prev = c
|
||||
}
|
||||
nv = append(nv, c)
|
||||
}
|
||||
|
||||
ch := strings.ToLower(strings.TrimRight(t[0], " \t")) + ":" + strings.Trim(string(nv), " \t")
|
||||
return ch, nil
|
||||
}
|
||||
|
||||
type header struct {
|
||||
key string // Key in original case.
|
||||
lkey string // Key in lower-case, for canonical case.
|
||||
value []byte // Literal header value, possibly spanning multiple lines, not modified in any way, including crlf, excluding leading key and colon.
|
||||
raw []byte // Like value, but including original leading key and colon. Ready for use as simple header canonicalized use.
|
||||
}
|
||||
|
||||
func parseHeaders(br *bufio.Reader) ([]header, int, error) {
|
||||
var o int
|
||||
var l []header
|
||||
var key, lkey string
|
||||
var value []byte
|
||||
var raw []byte
|
||||
for {
|
||||
line, err := readline(br)
|
||||
if err != nil {
|
||||
return nil, 0, err
|
||||
}
|
||||
o += len(line)
|
||||
if bytes.Equal(line, []byte("\r\n")) {
|
||||
break
|
||||
}
|
||||
if line[0] == ' ' || line[0] == '\t' {
|
||||
if len(l) == 0 && key == "" {
|
||||
return nil, 0, fmt.Errorf("malformed message, starts with space/tab")
|
||||
}
|
||||
value = append(value, line...)
|
||||
raw = append(raw, line...)
|
||||
continue
|
||||
}
|
||||
if key != "" {
|
||||
l = append(l, header{key, lkey, value, raw})
|
||||
}
|
||||
t := bytes.SplitN(line, []byte(":"), 2)
|
||||
if len(t) != 2 {
|
||||
return nil, 0, fmt.Errorf("malformed message, header without colon")
|
||||
}
|
||||
|
||||
key = strings.TrimRight(string(t[0]), " \t") // todo: where is this specified?
|
||||
// Check for valid characters. ../rfc/5322:1689 ../rfc/6532:193
|
||||
for _, c := range key {
|
||||
if c <= ' ' || c >= 0x7f {
|
||||
return nil, 0, fmt.Errorf("invalid header field name")
|
||||
}
|
||||
}
|
||||
if key == "" {
|
||||
return nil, 0, fmt.Errorf("empty header key")
|
||||
}
|
||||
lkey = strings.ToLower(key)
|
||||
value = append([]byte{}, t[1]...)
|
||||
raw = append([]byte{}, line...)
|
||||
}
|
||||
if key != "" {
|
||||
l = append(l, header{key, lkey, value, raw})
|
||||
}
|
||||
return l, o, nil
|
||||
}
|
||||
|
||||
func readline(r *bufio.Reader) ([]byte, error) {
|
||||
var buf []byte
|
||||
for {
|
||||
line, err := r.ReadBytes('\n')
|
||||
if err != nil {
|
||||
return nil, err
|
||||
}
|
||||
if bytes.HasSuffix(line, []byte("\r\n")) {
|
||||
if len(buf) == 0 {
|
||||
return line, nil
|
||||
}
|
||||
return append(buf, line...), nil
|
||||
}
|
||||
buf = append(buf, line...)
|
||||
}
|
||||
}
|
Reference in New Issue
Block a user