Provided by: libssl-doc_1.1.0g-2ubuntu4_all

**NAME**

BN_bn2binpad, BN_bn2bin, BN_bin2bn, BN_bn2lebinpad, BN_lebin2bn, BN_bn2hex, BN_bn2dec, BN_hex2bn, BN_dec2bn, BN_print, BN_print_fp, BN_bn2mpi, BN_mpi2bn - format conversions

**SYNOPSIS**

#include <openssl/bn.h> int BN_bn2bin(const BIGNUM *a, unsigned char *to); int BN_bn2binpad(const BIGNUM *a, unsigned char *to, int tolen); BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret); int BN_bn2lebinpad(const BIGNUM *a, unsigned char *to, int tolen); BIGNUM *BN_lebin2bn(const unsigned char *s, int len, BIGNUM *ret); char *BN_bn2hex(const BIGNUM *a); char *BN_bn2dec(const BIGNUM *a); int BN_hex2bn(BIGNUM **a, const char *str); int BN_dec2bn(BIGNUM **a, const char *str); int BN_print(BIO *fp, const BIGNUM *a); int BN_print_fp(FILE *fp, const BIGNUM *a); int BN_bn2mpi(const BIGNUM *a, unsigned char *to); BIGNUM *BN_mpi2bn(unsigned char *s, int len, BIGNUM *ret);

**DESCRIPTION**

BN_bn2bin()converts the absolute value ofainto big-endian form and stores it atto.tomust point to BN_num_bytes(a) bytes of memory.BN_bn2binpad()also converts the absolute value ofainto big-endian form and stores it atto.tolenindicates the length of the output bufferto. The result is padded with zeroes if necessary. Iftolenis less than BN_num_bytes(a) an error is returned.BN_bin2bn()converts the positive integer in big-endian form of lengthlenatsinto aBIGNUMand places it inret. Ifretis NULL, a newBIGNUMis created.BN_bn2lebinpad()andBN_bin2lbn()are identical toBN_bn2binpad()andBN_bin2bn()except the buffer is in little-endian format.BN_bn2hex()andBN_bn2dec()return printable strings containing the hexadecimal and decimal encoding ofarespectively. For negative numbers, the string is prefaced with a leading '-'. The string must be freed later usingOPENSSL_free().BN_hex2bn()takes as many characters as possible from the stringstr, including the leading character '-' which means negative, to form a valid hexadecimal number representation and converts them to aBIGNUMand stores it in **bn. If *bnis NULL, a newBIGNUMis created. Ifbnis NULL, it only computes the length of valid representation. A "negative zero" is converted to zero.BN_dec2bn()is the same using the decimal system.BN_print()andBN_print_fp()write the hexadecimal encoding ofa, with a leading '-' for negative numbers, to theBIOorFILEfp.BN_bn2mpi()andBN_mpi2bn()convertBIGNUMs from and to a format that consists of the number's length in bytes represented as a 4-byte big-endian number, and the number itself in big-endian format, where the most significant bit signals a negative number (the representation of numbers with the MSB set is prefixed with null byte).BN_bn2mpi()stores the representation ofaatto, wheretomust be large enough to hold the result. The size can be determined by calling BN_bn2mpi(a, NULL).BN_mpi2bn()converts thelenbytes long representation atsto aBIGNUMand stores it atret, or in a newly allocatedBIGNUMifretis NULL.

**RETURN** **VALUES**

BN_bn2bin()returns the length of the big-endian number placed atto.BN_bin2bn()returns theBIGNUM, NULL on error.BN_bn2binpad()returns the number of bytes written or -1 if the supplied buffer is too small.BN_bn2hex()andBN_bn2dec()return a null-terminated string, or NULL on error.BN_hex2bn()andBN_dec2bn()return the number of characters used in parsing, or 0 on error, in which case no newBIGNUMwill be created.BN_print_fp()andBN_print()return 1 on success, 0 on write errors.BN_bn2mpi()returns the length of the representation.BN_mpi2bn()returns theBIGNUM, and NULL on error. The error codes can be obtained byERR_get_error(3).

**SEE** **ALSO**

ERR_get_error(3),BN_zero(3),ASN1_INTEGER_to_BN(3),BN_num_bytes(3)

**COPYRIGHT**

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved. Licensed under the OpenSSL license (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>.