GPG commit validation (#1150)

* GPG commit validation

* Add translation

+ some little fix

* Move hash calc after retrieving of potential key + missing translation

* Add some little test

2 files changed, 302 insertions, 0 deletions

diff --git a/models/gpg_key.go b/models/gpg_key.go
index e7aac5162a..1c9d17d0e2 100644
--- a/models/gpg_key.go
+++ b/models/gpg_key.go
@@ -6,13 +6,21 @@ package models
 
 import (
 	"bytes"
+	"container/list"
+	"crypto"
 	"encoding/base64"
 	"fmt"
+	"hash"
+	"io"
 	"strings"
 	"time"
 
+	"code.gitea.io/git"
+	"code.gitea.io/gitea/modules/log"
+
 	"github.com/go-xorm/xorm"
 	"golang.org/x/crypto/openpgp"
+	"golang.org/x/crypto/openpgp/armor"
 	"golang.org/x/crypto/openpgp/packet"
 )
 
@@ -274,3 +282,181 @@ func DeleteGPGKey(doer *User, id int64) (err error) {
 
 	return nil
 }
+
+// CommitVerification represents a commit validation of signature
+type CommitVerification struct {
+	Verified    bool
+	Reason      string
+	SigningUser *User
+	SigningKey  *GPGKey
+}
+
+// SignCommit represents a commit with validation of signature.
+type SignCommit struct {
+	Verification *CommitVerification
+	*UserCommit
+}
+
+func readerFromBase64(s string) (io.Reader, error) {
+	bs, err := base64.StdEncoding.DecodeString(s)
+	if err != nil {
+		return nil, err
+	}
+	return bytes.NewBuffer(bs), nil
+}
+
+func populateHash(hashFunc crypto.Hash, msg []byte) (hash.Hash, error) {
+	h := hashFunc.New()
+	if _, err := h.Write(msg); err != nil {
+		return nil, err
+	}
+	return h, nil
+}
+
+// readArmoredSign read an armored signature block with the given type. https://sourcegraph.com/github.com/golang/crypto/-/blob/openpgp/read.go#L24:6-24:17
+func readArmoredSign(r io.Reader) (body io.Reader, err error) {
+	block, err := armor.Decode(r)
+	if err != nil {
+		return
+	}
+	if block.Type != openpgp.SignatureType {
+		return nil, fmt.Errorf("expected '" + openpgp.SignatureType + "', got: " + block.Type)
+	}
+	return block.Body, nil
+}
+
+func extractSignature(s string) (*packet.Signature, error) {
+	r, err := readArmoredSign(strings.NewReader(s))
+	if err != nil {
+		return nil, fmt.Errorf("Failed to read signature armor")
+	}
+	p, err := packet.Read(r)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to read signature packet")
+	}
+	sig, ok := p.(*packet.Signature)
+	if !ok {
+		return nil, fmt.Errorf("Packet is not a signature")
+	}
+	return sig, nil
+}
+
+func verifySign(s *packet.Signature, h hash.Hash, k *GPGKey) error {
+	//Check if key can sign
+	if !k.CanSign {
+		return fmt.Errorf("key can not sign")
+	}
+	//Decode key
+	b, err := readerFromBase64(k.Content)
+	if err != nil {
+		return err
+	}
+	//Read key
+	p, err := packet.Read(b)
+	if err != nil {
+		return err
+	}
+
+	//Check type
+	pkey, ok := p.(*packet.PublicKey)
+	if !ok {
+		return fmt.Errorf("key is not a public key")
+	}
+
+	return pkey.VerifySignature(h, s)
+}
+
+// ParseCommitWithSignature check if signature is good against keystore.
+func ParseCommitWithSignature(c *git.Commit) *CommitVerification {
+
+	if c.Signature != nil {
+
+		//Parsing signature
+		sig, err := extractSignature(c.Signature.Signature)
+		if err != nil { //Skipping failed to extract sign
+			log.Error(3, "SignatureRead err: %v", err)
+			return &CommitVerification{
+				Verified: false,
+				Reason:   "gpg.error.extract_sign",
+			}
+		}
+
+		//Find Committer account
+		committer, err := GetUserByEmail(c.Committer.Email)
+		if err != nil { //Skipping not user for commiter
+			log.Error(3, "NoCommitterAccount: %v", err)
+			return &CommitVerification{
+				Verified: false,
+				Reason:   "gpg.error.no_committer_account",
+			}
+		}
+
+		keys, err := ListGPGKeys(committer.ID)
+		if err != nil || len(keys) == 0 { //Skipping failed to get gpg keys of user
+			log.Error(3, "ListGPGKeys: %v", err)
+			return &CommitVerification{
+				Verified: false,
+				Reason:   "gpg.error.failed_retrieval_gpg_keys",
+			}
+		}
+
+		//Generating hash of commit
+		hash, err := populateHash(sig.Hash, []byte(c.Signature.Payload))
+		if err != nil { //Skipping ailed to generate hash
+			log.Error(3, "PopulateHash: %v", err)
+			return &CommitVerification{
+				Verified: false,
+				Reason:   "gpg.error.generate_hash",
+			}
+		}
+
+		for _, k := range keys {
+			//We get PK
+			if err := verifySign(sig, hash, k); err == nil {
+				return &CommitVerification{ //Everything is ok
+					Verified:    true,
+					Reason:      fmt.Sprintf("%s <%s> / %s", c.Committer.Name, c.Committer.Email, k.KeyID),
+					SigningUser: committer,
+					SigningKey:  k,
+				}
+			}
+			//And test also SubsKey
+			for _, sk := range k.SubsKey {
+				if err := verifySign(sig, hash, sk); err == nil {
+					return &CommitVerification{ //Everything is ok
+						Verified:    true,
+						Reason:      fmt.Sprintf("%s <%s> / %s", c.Committer.Name, c.Committer.Email, sk.KeyID),
+						SigningUser: committer,
+						SigningKey:  sk,
+					}
+				}
+			}
+		}
+		return &CommitVerification{ //Default at this stage
+			Verified: false,
+			Reason:   "gpg.error.no_gpg_keys_found",
+		}
+	}
+
+	return &CommitVerification{
+		Verified: false,                         //Default value
+		Reason:   "gpg.error.not_signed_commit", //Default value
+	}
+}
+
+// ParseCommitsWithSignature checks if signaute of commits are corresponding to users gpg keys.
+func ParseCommitsWithSignature(oldCommits *list.List) *list.List {
+	var (
+		newCommits = list.New()
+		e          = oldCommits.Front()
+	)
+	for e != nil {
+		c := e.Value.(UserCommit)
+		newCommits.PushBack(SignCommit{
+			UserCommit:   &c,
+			Verification: ParseCommitWithSignature(c.Commit),
+		})
+		e = e.Next()
+	}
+	return newCommits
+}
diff --git a/models/gpg_key_test.go b/models/gpg_key_test.go
index 1ef5838e31..d291ce91c0 100644
--- a/models/gpg_key_test.go
+++ b/models/gpg_key_test.go
@@ -46,3 +46,119 @@ MkM/fdpyc2hY7Dl/+qFmN5MG5yGmMpQcX+RNNR222ibNC1D3wg==
 	assert.Nil(t, err, "Could not parse a valid GPG armored key", key)
 	//TODO verify value of key
 }
+
+func TestExtractSignature(t *testing.T) {
+	testGPGArmor := `-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+=i9b7
+-----END PGP PUBLIC KEY BLOCK-----`
+	ekey, err := checkArmoredGPGKeyString(testGPGArmor)
+	assert.Nil(t, err, "Could not parse a valid GPG armored key", ekey)
+
+	pubkey := ekey.PrimaryKey
+	content, err := base64EncPubKey(pubkey)
+	assert.Nil(t, err, "Could not base64 encode a valid PublicKey content", ekey)
+
+	key := &GPGKey{
+		KeyID:             pubkey.KeyIdString(),
+		Content:           content,
+		Created:           pubkey.CreationTime,
+		CanSign:           pubkey.CanSign(),
+		CanEncryptComms:   pubkey.PubKeyAlgo.CanEncrypt(),
+		CanEncryptStorage: pubkey.PubKeyAlgo.CanEncrypt(),
+		CanCertify:        pubkey.PubKeyAlgo.CanSign(),
+	}
+
+	cannotsignkey := &GPGKey{
+		KeyID:             pubkey.KeyIdString(),
+		Content:           content,
+		Created:           pubkey.CreationTime,
+		CanSign:           false,
+		CanEncryptComms:   false,
+		CanEncryptStorage: false,
+		CanCertify:        false,
+	}
+
+	testGoodSigArmor := `-----BEGIN PGP SIGNATURE-----
+
+iQEzBAABCAAdFiEEEIOwJg/1vpF1itJ4roJVuKDYKOQFAljAiQIACgkQroJVuKDY
+KORvCgf6A/Ehh0r7QbO2tFEghT+/Ab+bN7jRN3zP9ed6/q/ophYmkrU0NibtbJH9
+AwFVdHxCmj78SdiRjaTKyevklXw34nvMftmvnOI4lBNUdw6KWl25/n/7wN0l2oZW
+rW3UawYpZgodXiLTYarfEimkDQmT67ArScjRA6lLbkEYKO0VdwDu+Z6yBUH3GWtm
+45RkXpnsF6AXUfuD7YxnfyyDE1A7g7zj4vVYUAfWukJjqow/LsCUgETETJOqj9q3
+52/oQDs04fVkIEtCDulcY+K/fKlukBPJf9WceNDEqiENUzN/Z1y0E+tJ07cSy4bk
+yIJb+d0OAaG8bxloO7nJq4Res1Qa8Q==
+=puvG
+-----END PGP SIGNATURE-----`
+	testGoodPayload := `tree 56ae8d2799882b20381fc11659db06c16c68c61a
+parent c7870c39e4e6b247235ca005797703ec4254613f
+author Antoine GIRARD <sapk@sapk.fr> 1489012989 +0100
+committer Antoine GIRARD <sapk@sapk.fr> 1489012989 +0100
+
+Goog GPG
+`
+
+	testBadSigArmor := `-----BEGIN PGP SIGNATURE-----
+
+iQEzBAABCAAdFiEE5yr4rn9ulbdMxJFiPYI/ySNrtNkFAljAiYkACgkQPYI/ySNr
+tNmDdQf+NXhVRiOGt0GucpjJCGrOnK/qqVUmQyRUfrqzVUdb/1/Ws84V5/wE547I
+6z3oxeBKFsJa1CtIlxYaUyVhYnDzQtphJzub+Aw3UG0E2ywiE+N7RCa1Ufl7pPxJ
+U0SD6gvNaeTDQV/Wctu8v8DkCtEd3N8cMCDWhvy/FQEDztVtzm8hMe0Vdm0ozEH6
+P0W93sDNkLC5/qpWDN44sFlYDstW5VhMrnF0r/ohfaK2kpYHhkPk7WtOoHSUwQSg
+c4gfhjvXIQrWFnII1Kr5jFGlmgNSR02qpb31VGkMzSnBhWVf2OaHS/kI49QHJakq
+AhVDEnoYLCgoDGg9c3p1Ll2452/c6Q==
+=uoGV
+-----END PGP SIGNATURE-----`
+	testBadPayload := `tree 3074ff04951956a974e8b02d57733b0766f7cf6c
+parent fd3577542f7ad1554c7c7c0eb86bb57a1324ad91
+author Antoine GIRARD <sapk@sapk.fr> 1489013107 +0100
+committer Antoine GIRARD <sapk@sapk.fr> 1489013107 +0100
+
+Unkonwn GPG key with good email
+`
+	//Reading Sign
+	goodSig, err := extractSignature(testGoodSigArmor)
+	assert.Nil(t, err, "Could not parse a valid GPG armored signature", testGoodSigArmor)
+	badSig, err := extractSignature(testBadSigArmor)
+	assert.Nil(t, err, "Could not parse a valid GPG armored signature", testBadSigArmor)
+
+	//Generating hash of commit
+	goodHash, err := populateHash(goodSig.Hash, []byte(testGoodPayload))
+	assert.Nil(t, err, "Could not generate a valid hash of payload", testGoodPayload)
+	badHash, err := populateHash(badSig.Hash, []byte(testBadPayload))
+	assert.Nil(t, err, "Could not generate a valid hash of payload", testBadPayload)
+
+	//Verify
+	err = verifySign(goodSig, goodHash, key)
+	assert.Nil(t, err, "Could not validate a good signature")
+	err = verifySign(badSig, badHash, key)
+	assert.NotNil(t, err, "Validate a bad signature")
+	err = verifySign(goodSig, goodHash, cannotsignkey)
+	assert.NotNil(t, err, "Validate a bad signature with a kay that can not sign")
+}