veryroundbird.house
1package crypto
2
3import (
4 "bytes"
5 "crypto/sha256"
6 "encoding/base64"
7 "fmt"
8 "strings"
9
10 "github.com/hiddeco/sshsig"
11 "golang.org/x/crypto/ssh"
12 "tangled.sh/tangled.sh/core/types"
13)
14
15func VerifySignature(pubKey, signature, payload []byte) (error, bool) {
16 pub, _, _, _, err := ssh.ParseAuthorizedKey(pubKey)
17 if err != nil {
18 return fmt.Errorf("failed to parse public key: %w", err), false
19 }
20
21 sig, err := sshsig.Unarmor(signature)
22 if err != nil {
23 return fmt.Errorf("failed to parse signature: %w", err), false
24 }
25
26 buf := bytes.NewBuffer(payload)
27 // we use sha-512 because ed25519 keys require it internally; rsa keys support
28 // multiple algorithms but sha-512 is most secure, and git's ssh signing defaults
29 // to sha-512 for all key types anyway.
30 err = sshsig.Verify(buf, sig, pub, sshsig.HashSHA512, "git")
31 return err, err == nil
32}
33
34// VerifyCommitSignature reconstructs the payload used to sign a commit. This is
35// essentially the git cat-file output but without the gpgsig header.
36//
37// Caveats: signature verification will fail on commits with more than one parent,
38// i.e. merge commits, because types.NiceDiff doesn't carry more than one Parent field
39// and we are unable to reconstruct the payload correctly.
40//
41// Ideally this should directly operate on an *object.Commit.
42func VerifyCommitSignature(pubKey string, commit types.NiceDiff) (error, bool) {
43 signature := commit.Commit.PGPSignature
44
45 author := bytes.NewBuffer([]byte{})
46 committer := bytes.NewBuffer([]byte{})
47 commit.Commit.Author.Encode(author)
48 commit.Commit.Committer.Encode(committer)
49
50 payload := strings.Builder{}
51
52 fmt.Fprintf(&payload, "tree %s\n", commit.Commit.Tree)
53 if commit.Commit.Parent != "" {
54 fmt.Fprintf(&payload, "parent %s\n", commit.Commit.Parent)
55 }
56 fmt.Fprintf(&payload, "author %s\n", author.String())
57 fmt.Fprintf(&payload, "committer %s\n", committer.String())
58 if commit.Commit.ChangedId != "" {
59 fmt.Fprintf(&payload, "change-id %s\n", commit.Commit.ChangedId)
60 }
61 fmt.Fprintf(&payload, "\n%s", commit.Commit.Message)
62
63 return VerifySignature([]byte(pubKey), []byte(signature), []byte(payload.String()))
64}
65
66// SSHFingerprint computes the fingerprint of the supplied ssh pubkey.
67func SSHFingerprint(pubKey string) (string, error) {
68 pk, _, _, _, err := ssh.ParseAuthorizedKey([]byte(pubKey))
69 if err != nil {
70 return "", err
71 }
72
73 hash := sha256.Sum256(pk.Marshal())
74 return "SHA256:" + base64.StdEncoding.EncodeToString(hash[:]), nil
75}