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RSA_size.3ossl - Man Page

get RSA modulus size or security bits


 #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);


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



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.

Referenced By

BN_num_bytes.3ossl(3), RSA_get0_key.3ossl(3), RSA_meth_new.3ossl(3), RSA_public_encrypt.3ossl(3).

The man pages RSA_bits.3ossl(3) and RSA_security_bits.3ossl(3) are aliases of RSA_size.3ossl(3).

2024-04-04 3.2.1 OpenSSL