RSA_size(3)

RSA_size(3) | OpenSSL | RSA_size(3)

# NAME

RSA_size, RSA_bits, RSA_security_bits - get RSA modulus size or security bits

# SYNOPSIS

     #include <openssl/rsa.h>
     int RSA_bits(const RSA *rsa);

The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

     int RSA_size(const RSA *rsa);
     int RSA_security_bits(const RSA *rsa);

# DESCRIPTION

RSA_bits() returns the number of significant bits.

rsa and rsa->n must not be NULL.

The remaining functions described on this page are deprecated. Applications should instead use EVP_PKEY_get_size(3), EVP_PKEY_get_bits(3) and EVP_PKEY_get_security_bits(3).

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_security_bits() returns the number of security bits of the given rsa key. See BN_security_bits(3).

# RETURN VALUES

RSA_bits() returns the number of bits in the key.

RSA_size() returns the size of modulus in bytes.

RSA_security_bits() returns the number of security bits.

# SEE ALSO

BN_num_bits(3)

# HISTORY

The RSA_size() and RSA_security_bits() functions were deprecated in OpenSSL 3.0.

The RSA_bits() function was added in OpenSSL 1.1.0.

# COPYRIGHT

Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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>.

2025-07-01 | 3.5.1