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# /usr/man/cat.3/BN_pseudo_rand_range.3.Z

```

```

## NAME

```       BN_rand, BN_pseudo_rand, BN_rand_range, BN_pseudo_rand_range - generate
pseudo-random number

```

## SYNOPSIS

```        #include <openssl/bn.h>

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

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

```

## DESCRIPTION

```       BN_rand() generates a cryptographically strong pseudo-random number of
bits in length and stores it in rnd.  If bits is less than zero, or too
small to accomodate the requirements specified by the top and bottom
parameters, an error is returned.  If top is -1, the most significant
bit of the random number can be zero. If top is 0, it is set to 1, and
if top is 1, 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 true, the number will be odd. The value of
bits must be zero or greater. If bits is 1 then top cannot also be 1.

BN_pseudo_rand() does the same, but pseudo-random numbers generated by
this function are not necessarily unpredictable. They can be used for
non-cryptographic purposes and for certain purposes in cryptographic
protocols, but usually not for key generation etc.

BN_rand_range() generates a cryptographically strong pseudo-random num-
ber rnd in the range 0 <= rnd < range.  BN_pseudo_rand_range() does the
same, but is based on BN_pseudo_rand(), and hence numbers generated by
it are not necessarily unpredictable.

The PRNG must be seeded prior to calling BN_rand() or BN_rand_range().

```

## RETURN VALUES

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

```

## SEE ALSO

```       bn(3), ERR_get_error(3), rand(3), RAND_add(3), RAND_bytes(3)

```

## HISTORY

```       BN_rand() is available in all versions of SSLeay and OpenSSL.
BN_pseudo_rand() was added in OpenSSL 0.9.5. The top == -1 case and the
function BN_rand_range() were added in OpenSSL 0.9.6a.
BN_pseudo_rand_range() was added in OpenSSL 0.9.6c.

1.0.2t                            2019-09-10                        BN_rand(3)
See also BN_pseudo_rand(3)
See also BN_rand(3)
See also BN_rand_range(3)
```

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