RSA_generate_key() generates a key pair and returns it in a newly allocated RSA structure. The pseudo-random number generator must be seeded prior to calling RSA_generate_key().The modulus size will be num bits, and the public exponent will be e. Key sizes with num < 1024 should be considered insecure. The exponent is an odd number, typically 3, 17 or 65537.
A callback function may be used to provide feedback about the progress of the key generation. If callback is not NULL, it will be called as follows:
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While a random prime number is generated, it is called as described in BN_generate_prime(3).
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When the n-th randomly generated prime is rejected as not suitable for the key, callback(2, n, cb_arg) is called.
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When a random p has been found with p-1 relatively prime to e, it is called as callback(3, 0, cb_arg).
The process is then repeated for prime q with callback(3, 1, cb_arg).