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feat(v2): Allow to include external signatures in messages
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@lubux
lubux committed Sep 28, 2023
1 parent 55193c9 commit a9c0e0a
Showing 1 changed file with 95 additions and 17 deletions.
112 changes: 95 additions & 17 deletions openpgp/v2/write.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,9 @@
package v2

import (
"bytes"
"crypto"
goerrors "errors"
"hash"
"io"
"strconv"
Expand Down Expand Up @@ -221,6 +223,11 @@ type EncryptParams struct {
// SessionKey provides a session key to be used for encryption.
// If nil, a one-time session key is generated
SessionKey []byte
// OutsideSig allows to set a signature that should be included
// in the message to encrypt.
// Should only be used for exceptional cases.
// If nil, ignored.
OutsideSig []byte
// Config provides the config to be used.
// If Config is nil, sensible defaults will be used.
Config *packet.Config
Expand Down Expand Up @@ -383,8 +390,46 @@ func Encrypt(ciphertext io.Writer, to, toHidden []*Entity, signers []*Entity, hi
// that aids the recipients in processing the message. The resulting
// WriteCloser must be closed after the contents of the file have been
// written. If config is nil, sensible defaults will be used.
func writeAndSign(payload io.WriteCloser, candidateHashes [][]uint8, signEntities []*Entity, hints *FileHints, sigType packet.SignatureType, intendedRecipients []*packet.Recipient, config *packet.Config) (plaintext io.WriteCloser, err error) {
func writeAndSign(payload io.WriteCloser, candidateHashes [][]uint8, signEntities []*Entity, hints *FileHints, sigType packet.SignatureType, intendedRecipients []*packet.Recipient, outsideSig []byte, config *packet.Config) (plaintext io.WriteCloser, err error) {
var signers []*signatureContext
var numberOfOutsideSigs int

if outsideSig != nil {
outSigPacket, err := parseOutsideSig(outsideSig)
if err != nil {
return nil, err
}
opsVersion := 3
if outSigPacket.Version == 6 {
opsVersion = 6
}
opsOutside := &packet.OnePassSignature{
Version: opsVersion,
SigType: outSigPacket.SigType,
Hash: outSigPacket.Hash,
PubKeyAlgo: outSigPacket.PubKeyAlgo,
KeyId: *outSigPacket.IssuerKeyId,
IsLast: len(signEntities) == 0,
}
sigContext := signatureContext{
outsideSig: outSigPacket,
}
if outSigPacket.Version == 6 {
opsOutside.KeyFingerprint = outSigPacket.IssuerFingerprint
sigContext.salt = outSigPacket.Salt()
opsOutside.Salt = outSigPacket.Salt()
}
sigContext.h, sigContext.wrappedHash, err = hashForSignature(outSigPacket.Hash, sigType, sigContext.salt)
if err != nil {
return nil, err
}
if err := opsOutside.Serialize(payload); err != nil {
return nil, err
}
signers = append([]*signatureContext{&sigContext}, signers...)
numberOfOutsideSigs = 1
}

for signEntityIdx, signEntity := range signEntities {
if signEntity == nil {
continue
Expand Down Expand Up @@ -442,7 +487,7 @@ func writeAndSign(payload io.WriteCloser, candidateHashes [][]uint8, signEntitie
signers = append([]*signatureContext{&sigContext}, signers...)
}

if signEntities != nil && len(signers) < 1 {
if signEntities != nil && len(signEntities)+numberOfOutsideSigs != len(signers) {
return nil, errors.InvalidArgumentError("no valid signing key")
}

Expand All @@ -451,7 +496,7 @@ func writeAndSign(payload io.WriteCloser, candidateHashes [][]uint8, signEntitie
}

w := payload
if signers != nil {
if signers != nil || numberOfOutsideSigs > 0 {
// If we need to write a signature packet after the literal
// data then we need to stop literalData from closing
// encryptedData.
Expand All @@ -467,7 +512,7 @@ func writeAndSign(payload io.WriteCloser, candidateHashes [][]uint8, signEntitie
return nil, err
}

if signers != nil {
if signers != nil || numberOfOutsideSigs > 0 {
metadata := &packet.LiteralData{
Format: 'b',
FileName: hints.FileName,
Expand Down Expand Up @@ -640,7 +685,7 @@ func encryptDataAndSign(
if err != nil {
return nil, err
}
return writeAndSign(payload, candidateHashes, params.Signers, params.Hints, sigType, intendedRecipients, params.Config)
return writeAndSign(payload, candidateHashes, params.Signers, params.Hints, sigType, intendedRecipients, params.OutsideSig, params.Config)
}

type SignParams struct {
Expand All @@ -649,6 +694,11 @@ type SignParams struct {
Hints *FileHints
// TextSig indicates if signatures of type SigTypeText should be produced
TextSig bool
// OutsideSig allows to set a signature that should be included
// in an inline signed message.
// Should only be used for exceptional cases.
// If nil, ignored.
OutsideSig []byte
// Config provides the config to be used.
// If Config is nil, sensible defaults will be used.
Config *packet.Config
Expand All @@ -661,7 +711,7 @@ func SignWithParams(output io.Writer, signers []*Entity, params *SignParams) (in
if params == nil {
params = &SignParams{}
}
if len(signers) < 1 {
if len(signers) < 1 && params.OutsideSig == nil {
return nil, errors.InvalidArgumentError("no signer provided")
}
var candidateHashesPerSignature [][]uint8
Expand Down Expand Up @@ -708,7 +758,7 @@ func SignWithParams(output io.Writer, signers []*Entity, params *SignParams) (in
if err != nil {
return nil, err
}
return writeAndSign(payload, candidateHashesPerSignature, signers, params.Hints, sigType, nil, params.Config)
return writeAndSign(payload, candidateHashesPerSignature, signers, params.Hints, sigType, nil, params.OutsideSig, params.Config)
}

// Sign signs a message. The resulting WriteCloser must be closed after the
Expand Down Expand Up @@ -742,6 +792,7 @@ type signatureContext struct {
h hash.Hash
salt []byte // v6 only
signer *packet.PrivateKey
outsideSig *packet.Signature
}

func (s signatureWriter) Write(data []byte) (int, error) {
Expand All @@ -764,16 +815,21 @@ func (s signatureWriter) Close() error {
return err
}
for _, ctx := range s.signatureContexts {
sig := createSignaturePacket(&ctx.signer.PublicKey, s.sigType, s.config)
sig.Hash = ctx.hashType
sig.Metadata = s.metadata
sig.IntendedRecipients = s.intendedRecipients

if err := sig.SetSalt(ctx.salt); err != nil {
return err
}
if err := sig.Sign(ctx.h, ctx.signer, s.config); err != nil {
return err
var sig *packet.Signature
if ctx.outsideSig != nil {
// Signature that was supplied outside
sig = ctx.outsideSig
} else {
sig = createSignaturePacket(&ctx.signer.PublicKey, s.sigType, s.config)
sig.Hash = ctx.hashType
sig.Metadata = s.metadata
sig.IntendedRecipients = s.intendedRecipients
if err := sig.SetSalt(ctx.salt); err != nil {
return err
}
if err := sig.Sign(ctx.h, ctx.signer, s.config); err != nil {
return err
}
}
if err := sig.Serialize(s.encryptedData); err != nil {
return err
Expand Down Expand Up @@ -872,3 +928,25 @@ func selectHash(candidateHashes []byte, configuredHash crypto.Hash) (hash crypto
}
return
}

func parseOutsideSig(outsideSig []byte) (outSigPacket *packet.Signature, err error) {
var p packet.Packet
packets := packet.NewReader(bytes.NewReader(outsideSig))
p, err = packets.Next()
if goerrors.Is(err, io.EOF) {
return nil, errors.ErrUnknownIssuer
}
if err != nil {
return nil, err
}

var ok bool
outSigPacket, ok = p.(*packet.Signature)
if !ok {
return nil, errors.StructuralError("non signature packet found")
}
if outSigPacket.IssuerKeyId == nil {
return nil, errors.StructuralError("signature doesn't have an issuer")
}
return outSigPacket, nil
}

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