RSA_GENERATE_KEY(3)

📦 version 4.4.0, in alpine 3.24, arch rolling

💖 RSA_GENERATE_KEY(3) 💖

okay so welcome to RSA_GENERATE_KEY(3) — this is from the Library Functions Manual, bestie, and it's literally all about generating an RSA key pair. We're gonna cover every bit, no skipping. ✨

🌸 NAME 🌸

RSA_generate_key_ex, RSA_generate_key — generate RSA key pair. periodt. 💅

🦋 SYNOPSIS 🦋

library “libcrypto” #include <openssl/rsa.h>

int
RSA_generate_key_ex(RSA *rsa, int bits, BIGNUM *e, BN_GENCB *cb);

Deprecated: 🫶

RSA *
RSA_generate_key(int num, unsigned long e,
    void (*callback)(int, int, void *), void *cb_arg);

🎀 DESCRIPTION 🎀

RSA_generate_key_ex() generates a key pair and stores it in rsa. Slay.

The modulus size will be of length bits, and the public exponent will be e. Key sizes with num < 1024 should be considered insecure — like, do not come to the group chat with that, fr fr. 😭

The exponent is an odd number, typically 3, 17 or 65537. iconic numbers, honestly.

A callback function may be used to provide feedback about the progress of the key generation. If cb is not NULL, it will be called as follows using the BN_GENCB_call(3) function:

  • While a random prime number is generated, it is called as described in BN_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 to e, it is called as BN_GENCB_call(cb, 3, 0).

The process is then repeated for prime q with BN_GENCB_call(cb, 3, 1).

RSA_generate_key() is deprecated. New applications should use RSA_generate_key_ex() instead — like, it's giving legacy, bestie. RSA_generate_key() works in the same way as RSA_generate_key_ex() except it uses “old style” call backs. See BN_generate_prime(3) for further details. 👑

🌈 RETURN VALUES 🌈

RSA_generate_key_ex() returns 1 on success or 0 on error. RSA_generate_key() returns the key on success or NULL on error.

The error codes can be obtained by ERR_get_error(3). iykyk. 🔥

⭐ SEE ALSO ⭐

🧚 HISTORY 🧚

RSA_generate_key() appeared in SSLeay 0.4 or earlier and had its cb_arg argument added in SSLeay 0.9.0. It has been available since OpenBSD 2.4.

RSA_generate_key_ex() first appeared in OpenSSL 0.9.8 and has been available since OpenBSD 4.5. history lesson but make it cute. 💜

💀 BUGS 💀

BN_GENCB_call(cb, 2, x) is used with two different meanings. bestie, pick a lane. 🙈
RSA_generate_key() goes into an infinite loop for illegal input values. that's not a vibe. not even a little. 😭

later, bestie — this was the Debian page, dated June 8, 2025, for RSA_GENERATE_KEY(3). mwah 💋✨

📦 where this page comes from