rsa: Verify RSA padding programatically

[platform/kernel/u-boot.git] / lib / rsa / rsa-verify.c

diff --git a/lib/rsa/rsa-verify.c b/lib/rsa/rsa-verify.c
index 5418f59..ee8988d 100644 (file)
--- a/lib/rsa/rsa-verify.c
+++ b/lib/rsa/rsa-verify.c
@@ -25,6 +25,40 @@
 #define RSA_DEFAULT_PUBEXP     65537
 
 /**
+ * rsa_verify_padding() - Verify RSA message padding is valid
+ *
+ * Verify a RSA message's padding is consistent with PKCS1.5
+ * padding as described in the RSA PKCS#1 v2.1 standard.
+ *
+ * @msg:       Padded message
+ * @pad_len:   Number of expected padding bytes
+ * @algo:      Checksum algo structure having information on DER encoding etc.
+ * @return 0 on success, != 0 on failure
+ */
+static int rsa_verify_padding(const uint8_t *msg, const int pad_len,
+                             struct checksum_algo *algo)
+{
+       int ff_len;
+       int ret;
+
+       /* first byte must be 0x00 */
+       ret = *msg++;
+       /* second byte must be 0x01 */
+       ret |= *msg++ ^ 0x01;
+       /* next ff_len bytes must be 0xff */
+       ff_len = pad_len - algo->der_len - 3;
+       ret |= *msg ^ 0xff;
+       ret |= memcmp(msg, msg+1, ff_len-1);
+       msg += ff_len;
+       /* next byte must be 0x00 */
+       ret |= *msg++;
+       /* next der_len bytes must match der_prefix */
+       ret |= memcmp(msg, algo->der_prefix, algo->der_len);
+
+       return ret;
+}
+
+/**
  * rsa_verify_key() - Verify a signature against some data using RSA Key
  *
  * Verify a RSA PKCS1.5 signature against an expected hash using
@@ -83,11 +117,11 @@ static int rsa_verify_key(struct key_prop *prop, const uint8_t *sig,
                return ret;
        }
 
-       padding = algo->rsa_padding;
        pad_len = algo->key_len - algo->checksum_len;
 
        /* Check pkcs1.5 padding bytes. */
-       if (memcmp(buf, padding, pad_len)) {
+       ret = rsa_verify_padding(buf, pad_len, algo);
+       if (ret) {
                debug("In RSAVerify(): Padding check failed!\n");
                return -EINVAL;
        }