Add SHA256 fingerprint utils and helpers (#41)

crypto/key.go

@@ -3,6 +3,7 @@ package crypto
 import (
 	"bytes"
 	"crypto"
+	"crypto/sha256"
 	"encoding/hex"
 	"fmt"
 	"io"
@@ -14,9 +15,9 @@ import (
 	"github.com/ProtonMail/gopenpgp/v2/constants"
 	"github.com/pkg/errors"
 
-	"golang.org/x/crypto/openpgp"
+	openpgp "golang.org/x/crypto/openpgp"
 	xarmor "golang.org/x/crypto/openpgp/armor"
-	"golang.org/x/crypto/openpgp/packet"
+	packet "golang.org/x/crypto/openpgp/packet"
 )
 
 // Key contains a single private or public key
@@ -321,8 +322,27 @@ func (key *Key) GetFingerprint() string {
 	return hex.EncodeToString(key.entity.PrimaryKey.Fingerprint[:])
 }
 
+// GetSHA256Fingerprints computes the SHA256 fingerprints of the key and subkeys
+func (key *Key) GetSHA256Fingerprints() (fingerprints []string) {
+	fingerprints = append(fingerprints, hex.EncodeToString(getSHA256FingerprintBytes(key.entity.PrimaryKey)))
+	for _, sub := range key.entity.Subkeys {
+		fingerprints = append(fingerprints, hex.EncodeToString(getSHA256FingerprintBytes(sub.PublicKey)))
+	}
+	return
+}
+
 // --- Internal methods
 
+// getSHA256FingerprintBytes computes the SHA256 fingerprint of a public key object
+func getSHA256FingerprintBytes(pk *packet.PublicKey) []byte {
+	fingerPrint := sha256.New()
+
+	// Hashing can't return an error, and has already been done when parsing the key,
+	// hence the error is nil
+	_ = pk.SerializeForHash(fingerPrint)
+	return fingerPrint.Sum(nil)
+}
+
 // readFrom reads unarmored and armored keys from r and adds them to the keyring.
 func (key *Key) readFrom(r io.Reader, armored bool) error {
 	var err error

crypto/key_test.go

@@ -310,3 +310,16 @@ func TestGetArmoredPublicKey(t *testing.T) {
 
 	assert.Exactly(t, eb, b)
 }
+
+func TestGetSHA256FingerprintsV4(t *testing.T) {
+	publicKey, err := NewKeyFromArmored(readTestFile("keyring_publicKey", false))
+	if err != nil {
+		t.Fatal("Cannot unarmor key:", err)
+	}
+
+	sha256Fingerprints := publicKey.GetSHA256Fingerprints()
+
+	assert.Len(t, sha256Fingerprints, 2)
+	assert.Exactly(t, "d9ac0b857da6d2c8be985b251a9e3db31e7a1d2d832d1f07ebe838a9edce9c24", sha256Fingerprints[0])
+	assert.Exactly(t, "203dfba1f8442c17e59214d9cd11985bfc5cc8721bb4a71740dd5507e58a1a0d", sha256Fingerprints[1])
+}