- NAME
- SYNOPSIS
- DESCRIPTION
- NOTES
- RETURN VALUES
- SEE ALSO
- HISTORY
- COPYRIGHT

# NAME

BN_rand_ex, BN_rand, BN_priv_rand_ex, BN_priv_rand, BN_pseudo_rand, BN_rand_range_ex, BN_rand_range, BN_priv_rand_range_ex, BN_priv_rand_range, BN_pseudo_rand_range - generate pseudo-random number

# SYNOPSIS

     #include <openssl/bn.h>

     int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom, BN_CTX *ctx);
     int BN_rand(BIGNUM *rnd, int bits, int top, int bottom);

     int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom, BN_CTX *ctx);
     int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom);

     int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom);

     int BN_rand_range_ex(BIGNUM *rnd, BIGNUM *range, BN_CTX *ctx);
     int BN_rand_range(BIGNUM *rnd, BIGNUM *range);

     int BN_priv_rand_range_ex(BIGNUM *rnd, BIGNUM *range, BN_CTX *ctx);
     int BN_priv_rand_range(BIGNUM *rnd, BIGNUM *range);

     int BN_pseudo_rand_range(BIGNUM *rnd, BIGNUM *range);

# DESCRIPTION

`BN_rand_ex()` generate a cryptographically strong pseudo-random number of bits in length and stores it in rnd using the random number generator for the library context associated with ctx. The parameter ctx may be NULL in which case the default library context is used. If bits is less than zero, or too small to accommodate the requirements specified by the top and bottom parameters, an error is returned. The top parameters specifies requirements on the most significant bit of the generated number. If it is BN_RAND_TOP_ANY, there is no constraint. If it is BN_RAND_TOP_ONE, the top bit must be one. If it is BN_RAND_TOP_TWO, the two most significant bits of the number will be set to 1, so that the product of two such random numbers will always have 2*bits length. If bottom is BN_RAND_BOTTOM_ODD, the number will be odd; if it is BN_RAND_BOTTOM_ANY it can be odd or even. If bits is 1 then top cannot also be BN_RAND_FLG_TOPTWO.

`BN_rand()` is the same as `BN_rand_ex()` except that the default library context is always used.

`BN_rand_range_ex()` generates a cryptographically strong pseudo-random number rnd in the range 0 <= rnd < range using the random number generator for the library context associated with ctx. The parameter ctx may be NULL in which case the default library context is used.

`BN_rand_range()` is the same as `BN_rand_range_ex()` except that the default library context is always used.

`BN_priv_rand_ex()`, `BN_priv_rand()`, `BN_priv_rand_rand_ex()` and `BN_priv_rand_range()` have the same semantics as `BN_rand_ex()`, `BN_rand()`, `BN_rand_range_ex()` and `BN_rand_range()` respectively. They are intended to be used for generating values that should remain private, and mirror the same difference between RAND_bytes(3) and RAND_priv_bytes(3).

# NOTES

Always check the error return value of these functions and do not take randomness for granted: an error occurs if the CSPRNG has not been seeded with enough randomness to ensure an unpredictable byte sequence.

# RETURN VALUES

The functions return 1 on success, 0 on error. The error codes can be obtained by ERR_get_error(3).

# SEE ALSO

ERR_get_error(3), RAND_add(3), RAND_bytes(3), RAND_priv_bytes(3), RAND(7), RAND_DRBG(7)

# HISTORY

- Starting with OpenSSL release 1.1.0, `BN_pseudo_rand()` has been identical to `BN_rand()` and `BN_pseudo_rand_range()` has been identical to `BN_rand_range()`. The "pseudo" functions should not be used and may be deprecated in a future release.

- The `BN_priv_rand()` and `BN_priv_rand_range()` functions were added in OpenSSL 1.1.1.

- The `BN_rand_ex()`, `BN_priv_rand_ex()`, `BN_rand_range_ex()` and `BN_priv_rand_range_ex()` functions were added in OpenSSL 3.0.

# COPYRIGHT

Copyright 2000-2019 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.