use save chunk advancing, check signature length

diff --git a/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c b/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c
index e241dba..1f3e307 100644 (file)
--- a/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c
+++ b/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c
@@ -140,11 +140,10 @@ static bool verify_emsa_pkcs1_signature(private_gmp_rsa_public_key_t *this,
        /* remove any preceding 0-bytes from signature */
        while (signature.len && *(signature.ptr) == 0x00)
        {
-               signature.len -= 1;
-               signature.ptr++;
+               signature = chunk_skip(signature, 1);
        }
        
-       if (signature.len > this->k)
+       if (signature.len == 0 || signature.len > this->k)
        {
                return INVALID_ARG;
        }
@@ -163,8 +162,7 @@ static bool verify_emsa_pkcs1_signature(private_gmp_rsa_public_key_t *this,
        {
                goto end;
        }
-       em.ptr += 2;
-       em.len -= 2;
+       em = chunk_skip(em, 2);
        
        /* find magic 0x00 */
        while (em.len > 0)
@@ -172,8 +170,7 @@ static bool verify_emsa_pkcs1_signature(private_gmp_rsa_public_key_t *this,
                if (*em.ptr == 0x00)
                {
                        /* found magic byte, stop */
-                       em.ptr++;
-                       em.len--;
+                       em = chunk_skip(em, 1);
                        break;
                }
                else if (*em.ptr != 0xFF)
@@ -181,8 +178,7 @@ static bool verify_emsa_pkcs1_signature(private_gmp_rsa_public_key_t *this,
                        /* bad padding, decryption failed ?!*/
                        goto end;
                }
-               em.ptr++;
-               em.len--;
+               em = chunk_skip(em, 1);
        }
 
        if (em.len == 0)