RSA_sign, RSA_verify - RSA signatures

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https://www.openssl.org/docs/manmaster/man3/RSA_sign.html
NAME

RSA_sign, RSA_verify - RSA signatures

SYNOPSIS #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 SHA1 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 mof 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).