[dev.boringcrypto.go1.8] crypto/internal/boring: handle RSA verification of short signatures

The standard Go crypto/rsa allows signatures to be shorter
than the RSA modulus and assumes leading zeros.
BoringCrypto does not, so supply the leading zeros explicitly.

This fixes the golang.org/x/crypto/openpgp tests.

Change-Id: Ic8b18d6beb0e02992a0474f5fdb2b73ccf7098cf
Reviewed-on: https://go-review.googlesource.com/62170
Reviewed-by: Adam Langley <agl@golang.org>
Reviewed-on: https://go-review.googlesource.com/65480
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

2 files changed, 35 insertions, 1 deletions

diff --git a/src/crypto/internal/boring/rsa.go b/src/crypto/internal/boring/rsa.go
index 0066520bf3..c31554de0c 100644
--- a/src/crypto/internal/boring/rsa.go
+++ b/src/crypto/internal/boring/rsa.go
@@ -283,9 +283,16 @@ func SignRSAPKCS1v15(priv *PrivateKeyRSA, h crypto.Hash, hashed []byte) ([]byte,
 }
 
 func VerifyRSAPKCS1v15(pub *PublicKeyRSA, h crypto.Hash, hashed, sig []byte) error {
+	size := int(C._goboringcrypto_RSA_size(pub.key))
+	if len(sig) < size {
+		// BoringCrypto requires sig to be same size as RSA key, so pad with leading zeros.
+		zsig := make([]byte, size)
+		copy(zsig[len(zsig)-len(sig):], sig)
+		sig = zsig
+	}
 	if h == 0 {
 		var outLen C.size_t
-		out := make([]byte, C._goboringcrypto_RSA_size(pub.key))
+		out := make([]byte, size)
 		if C._goboringcrypto_RSA_verify_raw(pub.key, &outLen, base(out), C.size_t(len(out)), base(sig), C.size_t(len(sig)), C.GO_RSA_PKCS1_PADDING) == 0 {
 			return fail("RSA_verify")
 		}
diff --git a/src/crypto/rsa/boring_test.go b/src/crypto/rsa/boring_test.go
index 7fbafee16e..290fe10a79 100644
--- a/src/crypto/rsa/boring_test.go
+++ b/src/crypto/rsa/boring_test.go
@@ -5,6 +5,7 @@
 package rsa
 
 import (
+	"crypto"
 	"crypto/rand"
 	"encoding/asn1"
 	"reflect"
@@ -38,3 +39,29 @@ func TestBoringDeepEqual(t *testing.T) {
 		t.Fatalf("DeepEqual compared boring fields")
 	}
 }
+
+func TestBoringVerify(t *testing.T) {
+	// This changed behavior and broke golang.org/x/crypto/openpgp.
+	// Go accepts signatures without leading 0 padding, while BoringCrypto does not.
+	// So the Go wrappers must adapt.
+	key := &PublicKey{
+		N: bigFromHex("c4fdf7b40a5477f206e6ee278eaef888ca73bf9128a9eef9f2f1ddb8b7b71a4c07cfa241f028a04edb405e4d916c61d6beabc333813dc7b484d2b3c52ee233c6a79b1eea4e9cc51596ba9cd5ac5aeb9df62d86ea051055b79d03f8a4fa9f38386f5bd17529138f3325d46801514ea9047977e0829ed728e68636802796801be1"),
+		E: 65537,
+	}
+
+	hash := fromHex("019c5571724fb5d0e47a4260c940e9803ba05a44")
+	paddedHash := fromHex("3021300906052b0e03021a05000414019c5571724fb5d0e47a4260c940e9803ba05a44")
+
+	// signature is one byte shorter than key.N.
+	sig := fromHex("5edfbeb6a73e7225ad3cc52724e2872e04260d7daf0d693c170d8c4b243b8767bc7785763533febc62ec2600c30603c433c095453ede59ff2fcabeb84ce32e0ed9d5cf15ffcbc816202b64370d4d77c1e9077d74e94a16fb4fa2e5bec23a56d7a73cf275f91691ae1801a976fcde09e981a2f6327ac27ea1fecf3185df0d56")
+
+	err := VerifyPKCS1v15(key, 0, paddedHash, sig)
+	if err != nil {
+		t.Errorf("raw: %v", err)
+	}
+
+	err = VerifyPKCS1v15(key, crypto.SHA1, hash, sig)
+	if err != nil {
+		t.Errorf("sha1: %v", err)
+	}
+}