deterministic_nonce.c
/*
* Copyright 2022-2023 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <openssl/bn.h>
#include <openssl/evp.h>
#include <openssl/core_names.h>
#include <openssl/kdf.h>
#include "internal/deterministic_nonce.h"
/*
* Convert a Bit String to an Integer (See RFC 6979 Section 2.3.2)
*
* Params:
* out The returned Integer as a BIGNUM
* qlen_bits The maximum size of the returned integer in bits. The returned
* Integer is shifted right if inlen is larger than qlen_bits..
* in, inlen The input Bit String (in bytes).
* Returns: 1 if successful, or 0 otherwise.
*/
static int bits2int(BIGNUM *out, int qlen_bits,
const unsigned char *in, size_t inlen)
{
int blen_bits = inlen * 8;
int shift;
if (BN_bin2bn(in, (int)inlen, out) == NULL)
return 0;
shift = blen_bits - qlen_bits;
if (shift > 0)
return BN_rshift(out, out, shift);
return 1;
}
/*
* Convert an Integer to an Octet String (See RFC 6979 2.3.3).
* The value is zero padded if required.
*
* Params:
* out The returned Octet String
* num The input Integer
* rlen The required size of the returned Octet String in bytes
* Returns: 1 if successful, or 0 otherwise.
*/
static int int2octets(unsigned char *out, const BIGNUM *num, int rlen)
{
return BN_bn2binpad(num, out, rlen) >= 0;
}
/*
* Convert a Bit String to an Octet String (See RFC 6979 Section 2.3.4)
*
* Params:
* out The returned octet string.
* q The modulus
* qlen_bits The length of q in bits
* rlen The value of qlen_bits rounded up to the nearest 8 bits.
* in, inlen The input bit string (in bytes)
* Returns: 1 if successful, or 0 otherwise.
*/
static int bits2octets(unsigned char *out, const BIGNUM *q, int qlen_bits,
int rlen, const unsigned char *in, size_t inlen)
{
int ret = 0;
BIGNUM *z = BN_new();
if (z == NULL
|| !bits2int(z, qlen_bits, in, inlen))
goto err;
/* z2 = z1 mod q (Do a simple subtract, since z1 < 2^qlen_bits) */
if (BN_cmp(z, q) >= 0
&& !BN_usub(z, z, q))
goto err;
ret = int2octets(out, z, rlen);
err:
BN_free(z);
return ret;
}
/*
* Setup a KDF HMAC_DRBG object using fixed entropy and nonce data.
*
* Params:
* digestname The digest name for the HMAC
* entropy, entropylen A fixed input entropy buffer
* nonce, noncelen A fixed input nonce buffer
* libctx, propq Are used for fetching algorithms
*
* Returns: The created KDF HMAC_DRBG object if successful, or NULL otherwise.
*/
static EVP_KDF_CTX *kdf_setup(const char *digestname,
const unsigned char *entropy, size_t entropylen,
const unsigned char *nonce, size_t noncelen,
OSSL_LIB_CTX *libctx, const char *propq)
{
EVP_KDF_CTX *ctx = NULL;
EVP_KDF *kdf = NULL;
OSSL_PARAM params[5], *p;
kdf = EVP_KDF_fetch(libctx, "HMAC-DRBG-KDF", propq);
ctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);
if (ctx == NULL)
goto err;
p = params;
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
(char *)digestname, 0);
if (propq != NULL)
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_PROPERTIES,
(char *)propq, 0);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_HMACDRBG_ENTROPY,
(void *)entropy, entropylen);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_HMACDRBG_NONCE,
(void *)nonce, noncelen);
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_CTX_set_params(ctx, params) <= 0)
goto err;
return ctx;
err:
EVP_KDF_CTX_free(ctx);
return NULL;
}
/*
* Generate a Deterministic nonce 'k' for DSA/ECDSA as defined in
* RFC 6979 Section 3.3. "Alternate Description of the Generation of k"
*
* Params:
* out Returns the generated deterministic nonce 'k'
* q A large prime number used for modulus operations for DSA and ECDSA.
* priv The private key in the range [1, q-1]
* hm, hmlen The digested message buffer in bytes
* digestname The digest name used for signing. It is used as the HMAC digest.
* libctx, propq Used for fetching algorithms
*
* Returns: 1 if successful, or 0 otherwise.
*/
int ossl_gen_deterministic_nonce_rfc6979(BIGNUM *out, const BIGNUM *q,
const BIGNUM *priv,
const unsigned char *hm, size_t hmlen,
const char *digestname,
OSSL_LIB_CTX *libctx,
const char *propq)
{
EVP_KDF_CTX *kdfctx = NULL;
int ret = 0, rlen = 0, qlen_bits = 0;
unsigned char *entropyx = NULL, *nonceh = NULL, *T = NULL;
size_t allocsz = 0;
if (out == NULL)
return 0;
qlen_bits = BN_num_bits(q);
if (qlen_bits == 0)
return 0;
/* Note rlen used here is in bytes since the input values are byte arrays */
rlen = (qlen_bits + 7) / 8;
allocsz = 3 * rlen;
/* Use a single alloc for the buffers T, nonceh and entropyx */
T = (unsigned char *)OPENSSL_zalloc(allocsz);
if (T == NULL)
return 0;
nonceh = T + rlen;
entropyx = nonceh + rlen;
if (!int2octets(entropyx, priv, rlen)
|| !bits2octets(nonceh, q, qlen_bits, rlen, hm, hmlen))
goto end;
kdfctx = kdf_setup(digestname, entropyx, rlen, nonceh, rlen, libctx, propq);
if (kdfctx == NULL)
goto end;
do {
if (!EVP_KDF_derive(kdfctx, T, rlen, NULL)
|| !bits2int(out, qlen_bits, T, rlen))
goto end;
} while (BN_is_zero(out) || BN_is_one(out) || BN_cmp(out, q) >= 0);
ret = 1;
end:
EVP_KDF_CTX_free(kdfctx);
OPENSSL_clear_free(T, allocsz);
return ret;
}
