This generates a "mask" byte array of size mask_len bytes as a concatenation of digests, where each digest is calculated on a concatenation of an input seed and a running counter to fill up mask_len bytes - as described by RFC8017 sec B.2.1. "MGF1".
The mask is useful for RSA signing/verification process with encoding RSASSA-PSS. Reference: https://tools.ietf.org/html/rfc8017#appendix-B.2.1 Signed-off-by: Varad Gautam <varad.gau...@suse.com> --- crypto/rsa-psspad.c | 54 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 54 insertions(+) diff --git a/crypto/rsa-psspad.c b/crypto/rsa-psspad.c index eec303bb55b2d..ed5374c381513 100644 --- a/crypto/rsa-psspad.c +++ b/crypto/rsa-psspad.c @@ -51,6 +51,60 @@ static int psspad_set_sig_params(struct crypto_akcipher *tfm, return 0; } +/* MGF1 per RFC8017 B.2.1. */ +static int pkcs1_mgf1(u8 *seed, unsigned int seed_len, + struct shash_desc *desc, + u8 *mask, unsigned int mask_len) +{ + unsigned int pos, h_len, i, c; + u8 *tmp; + int ret = 0; + + h_len = crypto_shash_digestsize(desc->tfm); + + pos = i = 0; + while ((i < (mask_len / h_len) + 1) && pos < mask_len) { + /* Compute T = T || Hash(mgfSeed || C) into mask at pos. */ + c = cpu_to_be32(i); + + ret = crypto_shash_init(desc); + if (ret < 0) + goto out_err; + + ret = crypto_shash_update(desc, seed, seed_len); + if (ret < 0) + goto out_err; + + ret = crypto_shash_update(desc, (u8 *) &c, sizeof(c)); + if (ret < 0) + goto out_err; + + if (mask_len - pos >= h_len) { + ret = crypto_shash_final(desc, mask + pos); + pos += h_len; + } else { + tmp = kzalloc(h_len, GFP_KERNEL); + if (!tmp) { + ret = -ENOMEM; + goto out_err; + } + ret = crypto_shash_final(desc, tmp); + /* copy the last hash */ + memcpy(mask + pos, tmp, mask_len - pos); + kfree(tmp); + pos = mask_len; + } + if (ret < 0) { + goto out_err; + } + + i++; + } + +out_err: + return ret; +} + static int psspad_s_v_e_d(struct akcipher_request *req) { return -EOPNOTSUPP; -- 2.30.2
