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**NAME**

RSA_generate_key_ex, RSA_generate_key, RSA_generate_multi_prime_key - generate RSA key pair

**SYNOPSIS**

#include <openssl/rsa.h> int RSA_generate_key_ex(RSA *rsa, int bits, BIGNUM *e, BN_GENCB *cb); int RSA_generate_multi_prime_key(RSA *rsa, int bits, int primes, BIGNUM *e, BN_GENCB *cb); Deprecated: #if OPENSSL_API_COMPAT < 0x00908000L RSA *RSA_generate_key(int num, unsigned long e, void (*callback)(int, int, void *), void *cb_arg); #endif

**DESCRIPTION**

RSA_generate_key_ex()generates a 2-prime RSA key pair and stores it in theRSAstructure provided inrsa. The pseudo-random number generator must be seeded prior to callingRSA_generate_key_ex().RSA_generate_multi_prime_key()generates a multi-prime RSA key pair and stores it in theRSAstructure provided inrsa. The number of primes is given by theprimesparameter. The pseudo-random number generator must be seeded prior to callingRSA_generate_multi_prime_key(). The modulus size will be of lengthbits, the number of primes to form the modulus will beprimes, and the public exponent will bee. Key sizes withnum< 1024 should be considered insecure. The exponent is an odd number, typically 3, 17 or 65537. In order to maintain adequate security level, the maximum number of permittedprimesdepends on modulus bit length: <1024 | >=1024 | >=4096 | >=8192 ------+--------+--------+------- 2 | 3 | 4 | 5 A callback function may be used to provide feedback about the progress of the key generation. Ifcbis notNULL, it will be called as follows using theBN_GENCB_call()function described on theBN_generate_prime(3) page.RSA_generate_prime()is similar toRSA_generate_prime_ex()but expects an old-style callback function; seeBN_generate_prime(3) for information on the old-style callback. · While a random prime number is generated, it is called as described inBN_generate_prime(3). · When the n-th randomly generated prime is rejected as not suitable for the key,BN_GENCB_call(cb,2,n)is called. · When a random p has been found with p-1 relatively prime toe, it is called asBN_GENCB_call(cb,3,0). The process is then repeated for prime q and other primes (if any) withBN_GENCB_call(cb,3,i)whereiindicates the i-th prime.

**RETURN** **VALUES**

RSA_generate_multi_prime_key()returns 1 on success or 0 on error.RSA_generate_key_ex()returns 1 on success or 0 on error. The error codes can be obtained byERR_get_error(3).RSA_generate_key()returns a pointer to the RSA structure orNULLif the key generation fails.

**BUGS**

BN_GENCB_call(cb,2,x)is used with two different meanings.

**SEE** **ALSO**

ERR_get_error(3),RAND_bytes(3),BN_generate_prime(3)

**HISTORY**

RSA_generate_key()was deprecated in OpenSSL 0.9.8; useRSA_generate_key_ex()instead.

**COPYRIGHT**

Copyright 2000-2018 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>.