crypto: asymmetric_keys - Adjust signature size calculation for NIST P521

[linux-block.git] / crypto / asymmetric_keys / public_key.c

diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
index e314fd57e6f88acffad4d4b4d8fa0b1e68071b9b..3474fb34ded9e5a756a11c5d118be4cbff5b9bed 100644 (file)
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c
@@ -234,6 +234,7 @@ static int software_key_query(const struct kernel_pkey_params *params,
        info->key_size = len * 8;
 
        if (strncmp(pkey->pkey_algo, "ecdsa", 5) == 0) {
+               int slen = len;
                /*
                 * ECDSA key sizes are much smaller than RSA, and thus could
                 * operate on (hashed) inputs that are larger than key size.
@@ -247,8 +248,19 @@ static int software_key_query(const struct kernel_pkey_params *params,
                 * Verify takes ECDSA-Sig (described in RFC 5480) as input,
                 * which is actually 2 'key_size'-bit integers encoded in
                 * ASN.1.  Account for the ASN.1 encoding overhead here.
+                *
+                * NIST P192/256/384 may prepend a '0' to a coordinate to
+                * indicate a positive integer. NIST P521 never needs it.
                 */
-               info->max_sig_size = 2 * (len + 3) + 2;
+               if (strcmp(pkey->pkey_algo, "ecdsa-nist-p521") != 0)
+                       slen += 1;
+               /* Length of encoding the x & y coordinates */
+               slen = 2 * (slen + 2);
+               /*
+                * If coordinate encoding takes at least 128 bytes then an
+                * additional byte for length encoding is needed.
+                */
+               info->max_sig_size = 1 + (slen >= 128) + 1 + slen;
        } else {
                info->max_data_size = len;
                info->max_sig_size = len;