RSA_SIZE(3) | Library Functions Manual | RSA_SIZE(3)

# NAME

`RSA_size`, `RSA_bits` — get the RSA modulus size

# SYNOPSIS

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

int
`RSA_size`(const RSA *rsa);

int
`RSA_bits`(const RSA *rsa);

# DESCRIPTION

`RSA_size`() returns the RSA modulus size in bytes. It can be used to determine how much memory must be allocated for an RSA encrypted value.

`RSA_bits`() returns the number of significant bits.

rsa and rsa->n must not be `NULL`.

# RETURN VALUES

The size.

# SEE ALSO

BN_num_bits(3), RSA_get0_key(3), RSA_new(3), RSA_security_bits(3)

# HISTORY

`RSA_size`() first appeared in SSLeay 0.4.4 and has been available since OpenBSD 2.4.

`RSA_bits`() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 6.3.

June 8, 2025 | Debian