RSA_NEW(3) | Library Functions Manual | RSA_NEW(3)

# NAME

`RSA_new`, `RSAPrivateKey_dup`, `RSAPublicKey_dup`, `RSA_up_ref`, `RSA_free` — allocate and free RSA objects

# SYNOPSIS

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

RSA *
`RSA_new`(void);

RSA *
`RSAPrivateKey_dup`(RSA *rsa);

RSA *
`RSAPublicKey_dup`(RSA *rsa);

int
`RSA_up_ref`(RSA *rsa);

void
`RSA_free`(RSA *rsa);

# DESCRIPTION

The RSA functions implement RSA public key encryption and signatures as defined in PKCS #1 v2.0 (RFC 2437).

`RSA_new`() allocates and initializes an RSA structure, setting the reference count to 1. It is equivalent to calling RSA_new_method(3) with a `NULL` argument.

`RSAPrivateKey_dup`() calls `RSA_new`() and copies the public and private key components from rsa into the new structure. `RSAPublicKey_dup`() does the same except that it copies the public key components only.

`RSA_up_ref`() increments the reference count by 1.

`RSA_free`() decrements the reference count by 1. If it reaches 0, it calls the optional finish function set up with RSA_meth_set_finish(3) and frees the RSA structure and its components. The key is erased before the memory is returned to the system. If rsa is a `NULL` pointer, no action occurs.

The RSA structure consists of several BIGNUM components. It can contain public as well as private RSA keys:

    typedef struct {
    	BIGNUM *n;		// public modulus
    	BIGNUM *e;		// public exponent
    	BIGNUM *d;		// private exponent
    	BIGNUM *p;		// secret prime factor
    	BIGNUM *q;		// secret prime factor
    	BIGNUM *dmp1;		// d mod (p-1)
    	BIGNUM *dmq1;		// d mod (q-1)
    	BIGNUM *iqmp;		// q^-1 mod p
    	// ...
    } RSA;

In public keys, the private exponent d and the related secret values p, q, dmp1, dmp2, and iqmp are `NULL`.

p, q, dmp1, dmq1, and iqmp may be `NULL` in private keys, but the RSA operations are much faster when these values are available.

Note that RSA keys may use non-standard RSA_METHOD implementations. In some cases, these BIGNUM values will not be used by the implementation or may be used for alternative data storage. For this reason, applications should generally avoid using RSA structure elements directly and instead use API functions to query or modify keys.

# RETURN VALUES

`RSA_new`(), `RSAPrivateKey_dup`(), and `RSAPublicKey_dup`() return a pointer to the newly allocated structure, or `NULL` if an error occurs. An error code can be obtained by ERR_get_error(3).

`RSA_up_ref`() returns 1 for success or 0 for failure.

# SEE ALSO

BN_new(3), crypto(3), d2i_RSAPublicKey(3), DH_new(3), DSA_new(3), EVP_PKEY_set1_RSA(3), RSA_blinding_on(3), RSA_check_key(3), RSA_generate_key(3), RSA_get0_key(3), RSA_get_ex_new_index(3), RSA_meth_new(3), RSA_padding_add_PKCS1_type_1(3), RSA_pkey_ctx_ctrl(3), RSA_print(3), RSA_private_encrypt(3), RSA_PSS_PARAMS_new(3), RSA_public_encrypt(3), RSA_security_bits(3), RSA_set_method(3), RSA_sign(3), RSA_sign_ASN1_OCTET_STRING(3), RSA_size(3)

# STANDARDS

SSL, PKCS #1 v2.0

RSA was covered by a US patent which expired in September 2000.

# HISTORY

`RSA_new`() and `RSA_free`() appeared in SSLeay 0.4 or earlier. `RSAPrivateKey_dup`() first appeared in SSLeay 0.5.1 and `RSAPublicKey_dup`() in SSLeay 0.5.2. These functions have been available since OpenBSD 2.4.

`RSA_up_ref`() first appeared in OpenSSL 0.9.7 and has been available since OpenBSD 3.2.

June 8, 2025 | Debian