RSA_SIGN(3) | Library Functions Manual | RSA_SIGN(3)

# NAME

`RSA_sign`, `RSA_verify` — RSA signatures

# SYNOPSIS

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

int
`RSA_sign`(int type, const unsigned char *m, unsigned int m_len, unsigned char *sigret, unsigned int *siglen, RSA *rsa);

int
`RSA_verify`(int type, const unsigned char *m, unsigned int m_len, unsigned char *sigbuf, unsigned int siglen, RSA *rsa);

# DESCRIPTION

`RSA_sign`() signs the message digest m of size m_len using the private key rsa using RSASSA-PKCS1-v1_5 as specified in RFC 3447. It stores the signature in sigret and the signature size in siglen. sigret must point to `RSA_size`(rsa) bytes of memory. Note that PKCS #1 adds meta-data, placing limits on the size of the key that can be used. See RSA_private_encrypt(3) for lower-level operations.

type denotes the message digest algorithm that was used to generate m. If type is NID_md5_sha1, an SSL signature (MD5 and SHA-1 message digests with PKCS #1 padding and no algorithm identifier) is created.

`RSA_verify`() verifies that the signature sigbuf of size siglen matches a given message digest m of size m_len. type denotes the message digest algorithm that was used to generate the signature. rsa is the signer's public key.

# RETURN VALUES

`RSA_sign`() returns 1 on success. `RSA_verify`() returns 1 on successful verification.

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

# SEE ALSO

RSA_meth_set_sign(3), RSA_new(3), RSA_private_encrypt(3), RSA_public_decrypt(3)

# STANDARDS

SSL, PKCS #1 v2.0

# HISTORY

`RSA_sign`() first appeared in SSLeay 0.4.4. `RSA_verify`() first appeared in SSLeay 0.6.0. Both functions have been available since OpenBSD 2.4.

June 8, 2025 | Debian