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@@ -1,5 +1,5 @@
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/*
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- * Copyright 1995-2023 The OpenSSL Project Authors. All Rights Reserved.
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+ * Copyright 1995-2024 The OpenSSL Project Authors. All Rights Reserved.
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*
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* Licensed under the Apache License 2.0 (the "License"). You may not use
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* this file except in compliance with the License. You can obtain a copy
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@@ -184,8 +184,8 @@ static int bnrand_range(BNRAND_FLAG flag, BIGNUM *r, const BIGNUM *range,
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} else {
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do {
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/* range = 11..._2 or range = 101..._2 */
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- if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, 0,
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- ctx))
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+ if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
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+ strength, ctx))
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return 0;
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if (!--count) {
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@@ -238,17 +238,63 @@ int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)
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# endif
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#endif
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+int ossl_bn_priv_rand_range_fixed_top(BIGNUM *r, const BIGNUM *range,
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+ unsigned int strength, BN_CTX *ctx)
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+{
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+ int n;
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+ int count = 100;
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+
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+ if (r == NULL) {
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+ ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);
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+ return 0;
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+ }
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+
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+ if (range->neg || BN_is_zero(range)) {
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+ ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);
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+ return 0;
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+ }
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+
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+ n = BN_num_bits(range); /* n > 0 */
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+
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+ /* BN_is_bit_set(range, n - 1) always holds */
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+
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+ if (n == 1) {
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+ BN_zero(r);
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+ } else {
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+ BN_set_flags(r, BN_FLG_CONSTTIME);
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+ do {
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+ if (!bnrand(PRIVATE, r, n + 1, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY,
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+ strength, ctx))
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+ return 0;
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+
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+ if (!--count) {
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+ ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
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+ return 0;
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+ }
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+ ossl_bn_mask_bits_fixed_top(r, n);
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+ }
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+ while (BN_ucmp(r, range) >= 0);
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+#ifdef BN_DEBUG
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+ /* With BN_DEBUG on a fixed top number cannot be returned */
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+ bn_correct_top(r);
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+#endif
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+ }
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+
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+ return 1;
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+}
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+
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/*
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- * BN_generate_dsa_nonce generates a random number 0 <= out < range. Unlike
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- * BN_rand_range, it also includes the contents of |priv| and |message| in
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- * the generation so that an RNG failure isn't fatal as long as |priv|
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+ * ossl_bn_gen_dsa_nonce_fixed_top generates a random number 0 <= out < range.
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+ * Unlike BN_rand_range, it also includes the contents of |priv| and |message|
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+ * in the generation so that an RNG failure isn't fatal as long as |priv|
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* remains secret. This is intended for use in DSA and ECDSA where an RNG
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* weakness leads directly to private key exposure unless this function is
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* used.
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*/
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-int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
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- const BIGNUM *priv, const unsigned char *message,
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- size_t message_len, BN_CTX *ctx)
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+int ossl_bn_gen_dsa_nonce_fixed_top(BIGNUM *out, const BIGNUM *range,
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+ const BIGNUM *priv,
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+ const unsigned char *message,
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+ size_t message_len, BN_CTX *ctx)
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{
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EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
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/*
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@@ -258,20 +304,24 @@ int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
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unsigned char random_bytes[64];
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unsigned char digest[SHA512_DIGEST_LENGTH];
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unsigned done, todo;
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- /* We generate |range|+8 bytes of random output. */
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- const unsigned num_k_bytes = BN_num_bytes(range) + 8;
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+ /* We generate |range|+1 bytes of random output. */
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+ const unsigned num_k_bytes = BN_num_bytes(range) + 1;
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unsigned char private_bytes[96];
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unsigned char *k_bytes = NULL;
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+ const int max_n = 64; /* Pr(failure to generate) < 2^max_n */
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+ int n;
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int ret = 0;
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EVP_MD *md = NULL;
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OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);
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if (mdctx == NULL)
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- goto err;
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+ goto end;
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k_bytes = OPENSSL_malloc(num_k_bytes);
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if (k_bytes == NULL)
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- goto err;
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+ goto end;
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+ /* Ensure top byte is set to avoid non-constant time in bin2bn */
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+ k_bytes[0] = 0xff;
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/* We copy |priv| into a local buffer to avoid exposing its length. */
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if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {
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@@ -281,41 +331,60 @@ int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
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* length of the private key.
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*/
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ERR_raise(ERR_LIB_BN, BN_R_PRIVATE_KEY_TOO_LARGE);
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- goto err;
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+ goto end;
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}
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md = EVP_MD_fetch(libctx, "SHA512", NULL);
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if (md == NULL) {
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ERR_raise(ERR_LIB_BN, BN_R_NO_SUITABLE_DIGEST);
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- goto err;
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- }
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- for (done = 0; done < num_k_bytes;) {
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- if (RAND_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes), 0) <= 0)
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- goto err;
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-
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- if (!EVP_DigestInit_ex(mdctx, md, NULL)
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- || !EVP_DigestUpdate(mdctx, &done, sizeof(done))
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- || !EVP_DigestUpdate(mdctx, private_bytes,
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- sizeof(private_bytes))
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- || !EVP_DigestUpdate(mdctx, message, message_len)
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- || !EVP_DigestUpdate(mdctx, random_bytes, sizeof(random_bytes))
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- || !EVP_DigestFinal_ex(mdctx, digest, NULL))
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- goto err;
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-
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- todo = num_k_bytes - done;
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- if (todo > SHA512_DIGEST_LENGTH)
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- todo = SHA512_DIGEST_LENGTH;
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- memcpy(k_bytes + done, digest, todo);
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- done += todo;
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+ goto end;
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}
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+ for (n = 0; n < max_n; n++) {
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+ unsigned char i = 0;
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+
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+ for (done = 1; done < num_k_bytes;) {
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+ if (RAND_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes),
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+ 0) <= 0)
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+ goto end;
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+
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+ if (!EVP_DigestInit_ex(mdctx, md, NULL)
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+ || !EVP_DigestUpdate(mdctx, &i, sizeof(i))
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+ || !EVP_DigestUpdate(mdctx, private_bytes,
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+ sizeof(private_bytes))
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+ || !EVP_DigestUpdate(mdctx, message, message_len)
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+ || !EVP_DigestUpdate(mdctx, random_bytes,
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+ sizeof(random_bytes))
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+ || !EVP_DigestFinal_ex(mdctx, digest, NULL))
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+ goto end;
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+
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+ todo = num_k_bytes - done;
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+ if (todo > SHA512_DIGEST_LENGTH)
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+ todo = SHA512_DIGEST_LENGTH;
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+ memcpy(k_bytes + done, digest, todo);
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+ done += todo;
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+ ++i;
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+ }
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- if (!BN_bin2bn(k_bytes, num_k_bytes, out))
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- goto err;
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- if (BN_mod(out, out, range, ctx) != 1)
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- goto err;
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- ret = 1;
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+ if (!BN_bin2bn(k_bytes, num_k_bytes, out))
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+ goto end;
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- err:
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+ /* Clear out the top bits and rejection filter into range */
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+ BN_set_flags(out, BN_FLG_CONSTTIME);
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+ ossl_bn_mask_bits_fixed_top(out, BN_num_bits(range));
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+
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+ if (BN_ucmp(out, range) < 0) {
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+ ret = 1;
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+#ifdef BN_DEBUG
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+ /* With BN_DEBUG on a fixed top number cannot be returned */
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+ bn_correct_top(out);
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+#endif
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+ goto end;
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+ }
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+ }
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+ /* Failed to generate anything */
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+ ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);
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+
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+ end:
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EVP_MD_CTX_free(mdctx);
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EVP_MD_free(md);
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OPENSSL_clear_free(k_bytes, num_k_bytes);
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@@ -324,3 +393,20 @@ int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
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OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
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return ret;
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}
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+
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+int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
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+ const BIGNUM *priv, const unsigned char *message,
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+ size_t message_len, BN_CTX *ctx)
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+{
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+ int ret;
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+
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+ ret = ossl_bn_gen_dsa_nonce_fixed_top(out, range, priv, message,
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+ message_len, ctx);
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+ /*
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+ * This call makes the BN_generate_dsa_nonce non-const-time, thus we
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+ * do not use it internally. But fixed_top BNs currently cannot be returned
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+ * from public API calls.
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+ */
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+ bn_correct_top(out);
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+ return ret;
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+}
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