From ac4cf77b106feb9dfa4c0f192a4fe7f59818f48b Mon Sep 17 00:00:00 2001 From: Stefan Berger Date: Thu, 4 Apr 2024 10:18:55 -0400 Subject: crypto: asymmetric_keys - Adjust signature size calculation for NIST P521 Adjust the calculation of the maximum signature size for support of NIST P521. While existing curves may prepend a 0 byte to their coordinates (to make the number positive), NIST P521 will not do this since only the first bit in the most significant byte is used. If the encoding of the x & y coordinates requires at least 128 bytes then an additional byte is needed for the encoding of the length. Take this into account when calculating the maximum signature size. Reviewed-by: Lukas Wunner Tested-by: Lukas Wunner Reviewed-by: Jarkko Sakkinen Signed-off-by: Stefan Berger Signed-off-by: Herbert Xu --- crypto/asymmetric_keys/public_key.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'crypto/asymmetric_keys/public_key.c') diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c index e314fd57..3474fb34 100644 --- 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; -- cgit v1.2.3