/src/openssl/crypto/bn/bn_rand.c

Source
/*
 * Copyright 1995-2024 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 <stdio.h>
#include <time.h>
#include "internal/cryptlib.h"
#include "crypto/rand.h"
#include "bn_local.h"
#include <openssl/rand.h>
#include <openssl/sha.h>
#include <openssl/evp.h>

typedef enum bnrand_flag_e {
    NORMAL,
    TESTING,
    PRIVATE
} BNRAND_FLAG;

static int bnrand(BNRAND_FLAG flag, BIGNUM *rnd, int bits, int top, int bottom,
    unsigned int strength, BN_CTX *ctx)
{
    unsigned char *buf = NULL;
    int b, ret = 0, bit, bytes, mask;
    OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);

    if (bits == 0) {
        if (top != BN_RAND_TOP_ANY || bottom != BN_RAND_BOTTOM_ANY)
            goto toosmall;
        BN_zero(rnd);
        return 1;
    }
    if (bits < 0 || (bits == 1 && top > 0))
        goto toosmall;

    bytes = (bits + 7) / 8;
    bit = (bits - 1) % 8;
    mask = 0xff << (bit + 1);

    buf = OPENSSL_malloc(bytes);
    if (buf == NULL)
        goto err;

    /* make a random number and set the top and bottom bits */
    b = flag == NORMAL ? RAND_bytes_ex(libctx, buf, bytes, strength)
                       : RAND_priv_bytes_ex(libctx, buf, bytes, strength);
    if (b <= 0)
        goto err;

    if (flag == TESTING) {
        /*
         * generate patterns that are more likely to trigger BN library bugs
         */
        int i;
        unsigned char c;

        for (i = 0; i < bytes; i++) {
            if (RAND_bytes_ex(libctx, &c, 1, strength) <= 0)
                goto err;
            if (c >= 128 && i > 0)
                buf[i] = buf[i - 1];
            else if (c < 42)
                buf[i] = 0;
            else if (c < 84)
                buf[i] = 255;
        }
    }

    if (top >= 0) {
        if (top) {
            if (bit == 0) {
                buf[0] = 1;
                buf[1] |= 0x80;
            } else {
                buf[0] |= (3 << (bit - 1));
            }
        } else {
            buf[0] |= (1 << bit);
        }
    }
    buf[0] &= ~mask;
    if (bottom) /* set bottom bit if requested */
        buf[bytes - 1] |= 1;
    if (!BN_bin2bn(buf, bytes, rnd))
        goto err;
    ret = 1;
err:
    OPENSSL_clear_free(buf, bytes);
    bn_check_top(rnd);
    return ret;

toosmall:
    ERR_raise(ERR_LIB_BN, BN_R_BITS_TOO_SMALL);
    return 0;
}

int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
    unsigned int strength, BN_CTX *ctx)
{
    return bnrand(NORMAL, rnd, bits, top, bottom, strength, ctx);
}
#ifndef FIPS_MODULE
int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)
{
    return bnrand(NORMAL, rnd, bits, top, bottom, 0, NULL);
}

int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
{
    return bnrand(TESTING, rnd, bits, top, bottom, 0, NULL);
}
#endif

int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
    unsigned int strength, BN_CTX *ctx)
{
    return bnrand(PRIVATE, rnd, bits, top, bottom, strength, ctx);
}

#ifndef FIPS_MODULE
int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom)
{
    return bnrand(PRIVATE, rnd, bits, top, bottom, 0, NULL);
}
#endif

/* random number r:  0 <= r < range */
static int bnrand_range(BNRAND_FLAG flag, BIGNUM *r, const BIGNUM *range,
    unsigned int strength, BN_CTX *ctx)
{
    int n;
    int count = 100;

    if (r == NULL) {
        ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);
        return 0;
    }

    if (range->neg || BN_is_zero(range)) {
        ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);
        return 0;
    }

    n = BN_num_bits(range); /* n > 0 */

    /* BN_is_bit_set(range, n - 1) always holds */

    if (n == 1)
        BN_zero(r);
    else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {
        /*
         * range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer
         * than range
         */
        do {
            if (!bnrand(flag, r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
                    strength, ctx))
                return 0;

            /*
             * If r < 3*range, use r := r MOD range (which is either r, r -
             * range, or r - 2*range). Otherwise, iterate once more. Since
             * 3*range = 11..._2, each iteration succeeds with probability >=
             * .75.
             */
            if (BN_cmp(r, range) >= 0) {
                if (!BN_sub(r, r, range))
                    return 0;
                if (BN_cmp(r, range) >= 0)
                    if (!BN_sub(r, r, range))
                        return 0;
            }

            if (!--count) {
                ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
                return 0;
            }

        } while (BN_cmp(r, range) >= 0);
    } else {
        do {
            /* range = 11..._2  or  range = 101..._2 */
            if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
                    strength, ctx))
                return 0;

            if (!--count) {
                ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
                return 0;
            }
        } while (BN_cmp(r, range) >= 0);
    }

    bn_check_top(r);
    return 1;
}

int BN_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,
    BN_CTX *ctx)
{
    return bnrand_range(NORMAL, r, range, strength, ctx);
}

#ifndef FIPS_MODULE
int BN_rand_range(BIGNUM *r, const BIGNUM *range)
{
    return bnrand_range(NORMAL, r, range, 0, NULL);
}
#endif

int BN_priv_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,
    BN_CTX *ctx)
{
    return bnrand_range(PRIVATE, r, range, strength, ctx);
}

#ifndef FIPS_MODULE
int BN_priv_rand_range(BIGNUM *r, const BIGNUM *range)
{
    return bnrand_range(PRIVATE, r, range, 0, NULL);
}

#ifndef OPENSSL_NO_DEPRECATED_3_0
int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)
{
    return BN_rand(rnd, bits, top, bottom);
}

int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)
{
    return BN_rand_range(r, range);
}
#endif
#endif

int ossl_bn_priv_rand_range_fixed_top(BIGNUM *r, const BIGNUM *range,
    unsigned int strength, BN_CTX *ctx)
{
    int n;
    int count = 100;

    if (r == NULL) {
        ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);
        return 0;
    }

    if (range->neg || BN_is_zero(range)) {
        ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);
        return 0;
    }

    n = BN_num_bits(range); /* n > 0 */

    /* BN_is_bit_set(range, n - 1) always holds */

    if (n == 1) {
        BN_zero(r);
    } else {
        BN_set_flags(r, BN_FLG_CONSTTIME);
        do {
            if (!bnrand(PRIVATE, r, n + 1, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY,
                    strength, ctx))
                return 0;

            if (!--count) {
                ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
                return 0;
            }
            ossl_bn_mask_bits_fixed_top(r, n);
        } while (BN_ucmp(r, range) >= 0);
#ifdef BN_DEBUG
        /* With BN_DEBUG on a fixed top number cannot be returned */
        bn_correct_top(r);
#endif
    }

    return 1;
}

/*
 * ossl_bn_gen_dsa_nonce_fixed_top generates a random number 0 <= out < range.
 * Unlike BN_rand_range, it also includes the contents of |priv| and |message|
 * in the generation so that an RNG failure isn't fatal as long as |priv|
 * remains secret. This is intended for use in DSA and ECDSA where an RNG
 * weakness leads directly to private key exposure unless this function is
 * used.
 */
int ossl_bn_gen_dsa_nonce_fixed_top(BIGNUM *out, const BIGNUM *range,
    const BIGNUM *priv,
    const unsigned char *message,
    size_t message_len, BN_CTX *ctx)
{
    EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
    /*
     * We use 512 bits of random data per iteration to ensure that we have at
     * least |range| bits of randomness.
     */
    unsigned char random_bytes[64];
    unsigned char digest[SHA512_DIGEST_LENGTH];
    unsigned done, todo;
    /* We generate |range|+1 bytes of random output. */
    const unsigned num_k_bytes = BN_num_bytes(range) + 1;
    unsigned char private_bytes[96];
    unsigned char *k_bytes = NULL;
    const int max_n = 64; /* Pr(failure to generate) < 2^max_n */
    int n;
    int ret = 0;
    EVP_MD *md = NULL;
    OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);

    if (mdctx == NULL)
        goto end;

    k_bytes = OPENSSL_malloc(num_k_bytes);
    if (k_bytes == NULL)
        goto end;
    /* Ensure top byte is set to avoid non-constant time in bin2bn */
    k_bytes[0] = 0xff;

    /* We copy |priv| into a local buffer to avoid exposing its length. */
    if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {
        /*
         * No reasonable DSA or ECDSA key should have a private key this
         * large and we don't handle this case in order to avoid leaking the
         * length of the private key.
         */
        ERR_raise(ERR_LIB_BN, BN_R_PRIVATE_KEY_TOO_LARGE);
        goto end;
    }

    md = EVP_MD_fetch(libctx, "SHA512", NULL);
    if (md == NULL) {
        ERR_raise(ERR_LIB_BN, BN_R_NO_SUITABLE_DIGEST);
        goto end;
    }
    for (n = 0; n < max_n; n++) {
        unsigned char i = 0;

        for (done = 1; done < num_k_bytes;) {
            if (RAND_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes),
                    0)
                <= 0)
                goto end;

            if (!EVP_DigestInit_ex(mdctx, md, NULL)
                || !EVP_DigestUpdate(mdctx, &i, sizeof(i))
                || !EVP_DigestUpdate(mdctx, private_bytes,
                    sizeof(private_bytes))
                || !EVP_DigestUpdate(mdctx, message, message_len)
                || !EVP_DigestUpdate(mdctx, random_bytes,
                    sizeof(random_bytes))
                || !EVP_DigestFinal_ex(mdctx, digest, NULL))
                goto end;

            todo = num_k_bytes - done;
            if (todo > SHA512_DIGEST_LENGTH)
                todo = SHA512_DIGEST_LENGTH;
            memcpy(k_bytes + done, digest, todo);
            done += todo;
            ++i;
        }

        if (!BN_bin2bn(k_bytes, num_k_bytes, out))
            goto end;

        /* Clear out the top bits and rejection filter into range */
        BN_set_flags(out, BN_FLG_CONSTTIME);
        ossl_bn_mask_bits_fixed_top(out, BN_num_bits(range));

        if (BN_ucmp(out, range) < 0) {
            ret = 1;
#ifdef BN_DEBUG
            /* With BN_DEBUG on a fixed top number cannot be returned */
            bn_correct_top(out);
#endif
            goto end;
        }
    }
    /* Failed to generate anything */
    ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);

end:
    EVP_MD_CTX_free(mdctx);
    EVP_MD_free(md);
    OPENSSL_clear_free(k_bytes, num_k_bytes);
    OPENSSL_cleanse(digest, sizeof(digest));
    OPENSSL_cleanse(random_bytes, sizeof(random_bytes));
    OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
    return ret;
}

int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
    const BIGNUM *priv, const unsigned char *message,
    size_t message_len, BN_CTX *ctx)
{
    int ret;

    ret = ossl_bn_gen_dsa_nonce_fixed_top(out, range, priv, message,
        message_len, ctx);
    /*
     * This call makes the BN_generate_dsa_nonce non-const-time, thus we
     * do not use it internally. But fixed_top BNs currently cannot be returned
     * from public API calls.
     */
    bn_correct_top(out);
    return ret;
}

Coverage Report

Created: 2025-12-10 06:24

Line	Count	Source
1		/*
2		* Copyright 1995-2024 The OpenSSL Project Authors. All Rights Reserved.
3		*
4		* Licensed under the Apache License 2.0 (the "License"). You may not use
5		* this file except in compliance with the License. You can obtain a copy
6		* in the file LICENSE in the source distribution or at
7		* https://www.openssl.org/source/license.html
8		*/
9
10		#include <stdio.h>
11		#include <time.h>
12		#include "internal/cryptlib.h"
13		#include "crypto/rand.h"
14		#include "bn_local.h"
15		#include <openssl/rand.h>
16		#include <openssl/sha.h>
17		#include <openssl/evp.h>
18
19		typedef enum bnrand_flag_e {
20		NORMAL,
21		TESTING,
22		PRIVATE
23		} BNRAND_FLAG;
24
25		static int bnrand(BNRAND_FLAG flag, BIGNUM *rnd, int bits, int top, int bottom,
26		unsigned int strength, BN_CTX *ctx)
27	0	{
28	0	unsigned char *buf = NULL;
29	0	int b, ret = 0, bit, bytes, mask;
30	0	OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);
31
32	0	if (bits == 0) {
33	0	if (top != BN_RAND_TOP_ANY \|\| bottom != BN_RAND_BOTTOM_ANY)
34	0	goto toosmall;
35	0	BN_zero(rnd);
36	0	return 1;
37	0	}
38	0	if (bits < 0 \|\| (bits == 1 && top > 0))
39	0	goto toosmall;
40
41	0	bytes = (bits + 7) / 8;
42	0	bit = (bits - 1) % 8;
43	0	mask = 0xff << (bit + 1);
44
45	0	buf = OPENSSL_malloc(bytes);
46	0	if (buf == NULL)
47	0	goto err;
48
49		/* make a random number and set the top and bottom bits */
50	0	b = flag == NORMAL ? RAND_bytes_ex(libctx, buf, bytes, strength)
51	0	: RAND_priv_bytes_ex(libctx, buf, bytes, strength);
52	0	if (b <= 0)
53	0	goto err;
54
55	0	if (flag == TESTING) {
56		/*
57		* generate patterns that are more likely to trigger BN library bugs
58		*/
59	0	int i;
60	0	unsigned char c;
61
62	0	for (i = 0; i < bytes; i++) {
63	0	if (RAND_bytes_ex(libctx, &c, 1, strength) <= 0)
64	0	goto err;
65	0	if (c >= 128 && i > 0)
66	0	buf[i] = buf[i - 1];
67	0	else if (c < 42)
68	0	buf[i] = 0;
69	0	else if (c < 84)
70	0	buf[i] = 255;
71	0	}
72	0	}
73
74	0	if (top >= 0) {
75	0	if (top) {
76	0	if (bit == 0) {
77	0	buf[0] = 1;
78	0	buf[1] \|= 0x80;
79	0	} else {
80	0	buf[0] \|= (3 << (bit - 1));
81	0	}
82	0	} else {
83	0	buf[0] \|= (1 << bit);
84	0	}
85	0	}
86	0	buf[0] &= ~mask;
87	0	if (bottom) /* set bottom bit if requested */
88	0	buf[bytes - 1] \|= 1;
89	0	if (!BN_bin2bn(buf, bytes, rnd))
90	0	goto err;
91	0	ret = 1;
92	0	err:
93	0	OPENSSL_clear_free(buf, bytes);
94	0	bn_check_top(rnd);
95	0	return ret;
96
97	0	toosmall:
98	0	ERR_raise(ERR_LIB_BN, BN_R_BITS_TOO_SMALL);
99	0	return 0;
100	0	}
101
102		int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
103		unsigned int strength, BN_CTX *ctx)
104	0	{
105	0	return bnrand(NORMAL, rnd, bits, top, bottom, strength, ctx);
106	0	}
107		#ifndef FIPS_MODULE
108		int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)
109	0	{
110	0	return bnrand(NORMAL, rnd, bits, top, bottom, 0, NULL);
111	0	}
112
113		int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
114	0	{
115	0	return bnrand(TESTING, rnd, bits, top, bottom, 0, NULL);
116	0	}
117		#endif
118
119		int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
120		unsigned int strength, BN_CTX *ctx)
121	0	{
122	0	return bnrand(PRIVATE, rnd, bits, top, bottom, strength, ctx);
123	0	}
124
125		#ifndef FIPS_MODULE
126		int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom)
127	0	{
128	0	return bnrand(PRIVATE, rnd, bits, top, bottom, 0, NULL);
129	0	}
130		#endif
131
132		/* random number r: 0 <= r < range */
133		static int bnrand_range(BNRAND_FLAG flag, BIGNUM r, const BIGNUM range,
134		unsigned int strength, BN_CTX *ctx)
135	0	{
136	0	int n;
137	0	int count = 100;
138
139	0	if (r == NULL) {
140	0	ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);
141	0	return 0;
142	0	}
143
144	0	if (range->neg \|\| BN_is_zero(range)) {
145	0	ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);
146	0	return 0;
147	0	}
148
149	0	n = BN_num_bits(range); /* n > 0 */
150
151		/* BN_is_bit_set(range, n - 1) always holds */
152
153	0	if (n == 1)
154	0	BN_zero(r);
155	0	else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {
156		/*
157		* range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer
158		* than range
159		*/
160	0	do {
161	0	if (!bnrand(flag, r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
162	0	strength, ctx))
163	0	return 0;
164
165		/*
166		* If r < 3*range, use r := r MOD range (which is either r, r -
167		* range, or r - 2*range). Otherwise, iterate once more. Since
168		* 3*range = 11..._2, each iteration succeeds with probability >=
169		* .75.
170		*/
171	0	if (BN_cmp(r, range) >= 0) {
172	0	if (!BN_sub(r, r, range))
173	0	return 0;
174	0	if (BN_cmp(r, range) >= 0)
175	0	if (!BN_sub(r, r, range))
176	0	return 0;
177	0	}
178
179	0	if (!--count) {
180	0	ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
181	0	return 0;
182	0	}
183
184	0	} while (BN_cmp(r, range) >= 0);
185	0	} else {
186	0	do {
187		/* range = 11..._2 or range = 101..._2 */
188	0	if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
189	0	strength, ctx))
190	0	return 0;
191
192	0	if (!--count) {
193	0	ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
194	0	return 0;
195	0	}
196	0	} while (BN_cmp(r, range) >= 0);
197	0	}
198
199	0	bn_check_top(r);
200	0	return 1;
201	0	}
202
203		int BN_rand_range_ex(BIGNUM r, const BIGNUM range, unsigned int strength,
204		BN_CTX *ctx)
205	0	{
206	0	return bnrand_range(NORMAL, r, range, strength, ctx);
207	0	}
208
209		#ifndef FIPS_MODULE
210		int BN_rand_range(BIGNUM r, const BIGNUM range)
211	0	{
212	0	return bnrand_range(NORMAL, r, range, 0, NULL);
213	0	}
214		#endif
215
216		int BN_priv_rand_range_ex(BIGNUM r, const BIGNUM range, unsigned int strength,
217		BN_CTX *ctx)
218	0	{
219	0	return bnrand_range(PRIVATE, r, range, strength, ctx);
220	0	}
221
222		#ifndef FIPS_MODULE
223		int BN_priv_rand_range(BIGNUM r, const BIGNUM range)
224	0	{
225	0	return bnrand_range(PRIVATE, r, range, 0, NULL);
226	0	}
227
228		#ifndef OPENSSL_NO_DEPRECATED_3_0
229		int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)
230	0	{
231	0	return BN_rand(rnd, bits, top, bottom);
232	0	}
233
234		int BN_pseudo_rand_range(BIGNUM r, const BIGNUM range)
235	0	{
236	0	return BN_rand_range(r, range);
237	0	}
238		#endif
239		#endif
240
241		int ossl_bn_priv_rand_range_fixed_top(BIGNUM r, const BIGNUM range,
242		unsigned int strength, BN_CTX *ctx)
243	0	{
244	0	int n;
245	0	int count = 100;
246
247	0	if (r == NULL) {
248	0	ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);
249	0	return 0;
250	0	}
251
252	0	if (range->neg \|\| BN_is_zero(range)) {
253	0	ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);
254	0	return 0;
255	0	}
256
257	0	n = BN_num_bits(range); /* n > 0 */
258
259		/* BN_is_bit_set(range, n - 1) always holds */
260
261	0	if (n == 1) {
262	0	BN_zero(r);
263	0	} else {
264	0	BN_set_flags(r, BN_FLG_CONSTTIME);
265	0	do {
266	0	if (!bnrand(PRIVATE, r, n + 1, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY,
267	0	strength, ctx))
268	0	return 0;
269
270	0	if (!--count) {
271	0	ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
272	0	return 0;
273	0	}
274	0	ossl_bn_mask_bits_fixed_top(r, n);
275	0	} while (BN_ucmp(r, range) >= 0);
276		#ifdef BN_DEBUG
277		/* With BN_DEBUG on a fixed top number cannot be returned */
278		bn_correct_top(r);
279		#endif
280	0	}
281
282	0	return 1;
283	0	}
284
285		/*
286		* ossl_bn_gen_dsa_nonce_fixed_top generates a random number 0 <= out < range.
287		* Unlike BN_rand_range, it also includes the contents of \|priv\| and \|message\|
288		* in the generation so that an RNG failure isn't fatal as long as \|priv\|
289		* remains secret. This is intended for use in DSA and ECDSA where an RNG
290		* weakness leads directly to private key exposure unless this function is
291		* used.
292		*/
293		int ossl_bn_gen_dsa_nonce_fixed_top(BIGNUM out, const BIGNUM range,
294		const BIGNUM *priv,
295		const unsigned char *message,
296		size_t message_len, BN_CTX *ctx)
297	0	{
298	0	EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
299		/*
300		* We use 512 bits of random data per iteration to ensure that we have at
301		* least \|range\| bits of randomness.
302		*/
303	0	unsigned char random_bytes[64];
304	0	unsigned char digest[SHA512_DIGEST_LENGTH];
305	0	unsigned done, todo;
306		/* We generate \|range\|+1 bytes of random output. */
307	0	const unsigned num_k_bytes = BN_num_bytes(range) + 1;
308	0	unsigned char private_bytes[96];
309	0	unsigned char *k_bytes = NULL;
310	0	const int max_n = 64; /* Pr(failure to generate) < 2^max_n */
311	0	int n;
312	0	int ret = 0;
313	0	EVP_MD *md = NULL;
314	0	OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);
315
316	0	if (mdctx == NULL)
317	0	goto end;
318
319	0	k_bytes = OPENSSL_malloc(num_k_bytes);
320	0	if (k_bytes == NULL)
321	0	goto end;
322		/* Ensure top byte is set to avoid non-constant time in bin2bn */
323	0	k_bytes[0] = 0xff;
324
325		/* We copy \|priv\| into a local buffer to avoid exposing its length. */
326	0	if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {
327		/*
328		* No reasonable DSA or ECDSA key should have a private key this
329		* large and we don't handle this case in order to avoid leaking the
330		* length of the private key.
331		*/
332	0	ERR_raise(ERR_LIB_BN, BN_R_PRIVATE_KEY_TOO_LARGE);
333	0	goto end;
334	0	}
335
336	0	md = EVP_MD_fetch(libctx, "SHA512", NULL);
337	0	if (md == NULL) {
338	0	ERR_raise(ERR_LIB_BN, BN_R_NO_SUITABLE_DIGEST);
339	0	goto end;
340	0	}
341	0	for (n = 0; n < max_n; n++) {
342	0	unsigned char i = 0;
343
344	0	for (done = 1; done < num_k_bytes;) {
345	0	if (RAND_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes),
346	0	0)
347	0	<= 0)
348	0	goto end;
349
350	0	if (!EVP_DigestInit_ex(mdctx, md, NULL)
351	0	\|\| !EVP_DigestUpdate(mdctx, &i, sizeof(i))
352	0	\|\| !EVP_DigestUpdate(mdctx, private_bytes,
353	0	sizeof(private_bytes))
354	0	\|\| !EVP_DigestUpdate(mdctx, message, message_len)
355	0	\|\| !EVP_DigestUpdate(mdctx, random_bytes,
356	0	sizeof(random_bytes))
357	0	\|\| !EVP_DigestFinal_ex(mdctx, digest, NULL))
358	0	goto end;
359
360	0	todo = num_k_bytes - done;
361	0	if (todo > SHA512_DIGEST_LENGTH)
362	0	todo = SHA512_DIGEST_LENGTH;
363	0	memcpy(k_bytes + done, digest, todo);
364	0	done += todo;
365	0	++i;
366	0	}
367
368	0	if (!BN_bin2bn(k_bytes, num_k_bytes, out))
369	0	goto end;
370
371		/* Clear out the top bits and rejection filter into range */
372	0	BN_set_flags(out, BN_FLG_CONSTTIME);
373	0	ossl_bn_mask_bits_fixed_top(out, BN_num_bits(range));
374
375	0	if (BN_ucmp(out, range) < 0) {
376	0	ret = 1;
377		#ifdef BN_DEBUG
378		/* With BN_DEBUG on a fixed top number cannot be returned */
379		bn_correct_top(out);
380		#endif
381	0	goto end;
382	0	}
383	0	}
384		/* Failed to generate anything */
385	0	ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);
386
387	0	end:
388	0	EVP_MD_CTX_free(mdctx);
389	0	EVP_MD_free(md);
390	0	OPENSSL_clear_free(k_bytes, num_k_bytes);
391	0	OPENSSL_cleanse(digest, sizeof(digest));
392	0	OPENSSL_cleanse(random_bytes, sizeof(random_bytes));
393	0	OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
394	0	return ret;
395	0	}
396
397		int BN_generate_dsa_nonce(BIGNUM out, const BIGNUM range,
398		const BIGNUM priv, const unsigned char message,
399		size_t message_len, BN_CTX *ctx)
400	0	{
401	0	int ret;
402
403	0	ret = ossl_bn_gen_dsa_nonce_fixed_top(out, range, priv, message,
404	0	message_len, ctx);
405		/*
406		* This call makes the BN_generate_dsa_nonce non-const-time, thus we
407		* do not use it internally. But fixed_top BNs currently cannot be returned
408		* from public API calls.
409		*/
410	0	bn_correct_top(out);
411	0	return ret;
412	0	}