Cryptography and SSL/TLS Toolkit



RSA_padding_add_PKCS1_type_1, RSA_padding_check_PKCS1_type_1, RSA_padding_add_PKCS1_type_2, RSA_padding_check_PKCS1_type_2, RSA_padding_add_PKCS1_OAEP, RSA_padding_check_PKCS1_OAEP, RSA_padding_add_SSLv23, RSA_padding_check_SSLv23, RSA_padding_add_none, RSA_padding_check_none - asymmetric encryption padding


 #include <openssl/rsa.h>

 int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
    unsigned char *f, int fl);

 int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
    unsigned char *f, int fl, int rsa_len);

 int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
    unsigned char *f, int fl);

 int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
    unsigned char *f, int fl, int rsa_len);

 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
    unsigned char *f, int fl, unsigned char *p, int pl);

 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
    unsigned char *f, int fl, int rsa_len, unsigned char *p, int pl);

 int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
    unsigned char *f, int fl);

 int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
    unsigned char *f, int fl, int rsa_len);

 int RSA_padding_add_none(unsigned char *to, int tlen,
    unsigned char *f, int fl);

 int RSA_padding_check_none(unsigned char *to, int tlen,
    unsigned char *f, int fl, int rsa_len);


The RSA_padding_xxx_xxx() functions are called from the RSA encrypt, decrypt, sign and verify functions. Normally they should not be called from application programs.

However, they can also be called directly to implement padding for other asymmetric ciphers. RSA_padding_add_PKCS1_OAEP() and RSA_padding_check_PKCS1_OAEP() may be used in an application combined with RSA_NO_PADDING in order to implement OAEP with an encoding parameter.

RSA_padding_add_xxx() encodes fl bytes from f so as to fit into tlen bytes and stores the result at to. An error occurs if fl does not meet the size requirements of the encoding method.

The following encoding methods are implemented:


PKCS #1 v2.0 EMSA-PKCS1-v1_5 (PKCS #1 v1.5 block type 1); used for signatures


PKCS #1 v2.0 EME-PKCS1-v1_5 (PKCS #1 v1.5 block type 2)




PKCS #1 EME-PKCS1-v1_5 with SSL-specific modification


simply copy the data

The random number generator must be seeded prior to calling RSA_padding_add_xxx().

RSA_padding_check_xxx() verifies that the fl bytes at f contain a valid encoding for a rsa_len byte RSA key in the respective encoding method and stores the recovered data of at most tlen bytes (for RSA_NO_PADDING: of size tlen) at to.

For RSA_padding_xxx_OAEP(), p points to the encoding parameter of length pl. p may be NULL if pl is 0.


The RSA_padding_add_xxx() functions return 1 on success, 0 on error. The RSA_padding_check_xxx() functions return the length of the recovered data, -1 on error. Error codes can be obtained by calling ERR_get_error(3).


The RSA_padding_check_PKCS1_type_2() padding check leaks timing information which can potentially be used to mount a Bleichenbacher padding oracle attack. This is an inherent weakness in the PKCS #1 v1.5 padding design. Prefer PKCS1_OAEP padding. Otherwise it can be recommended to pass zero-padded f, so that fl equals to rsa_len, and if fixed by protocol, tlen being set to the expected length. In such case leakage would be minimal, it would take attacker's ability to observe memory access pattern with byte granilarity as it occurs, post-factum timing analysis won't do.


RSA_public_encrypt(3), RSA_private_decrypt(3), RSA_sign(3), RSA_verify(3)


RSA_padding_add_PKCS1_type_1(), RSA_padding_check_PKCS1_type_1(), RSA_padding_add_PKCS1_type_2(), RSA_padding_check_PKCS1_type_2(), RSA_padding_add_SSLv23(), RSA_padding_check_SSLv23(), RSA_padding_add_none() and RSA_padding_check_none() appeared in SSLeay 0.9.0.

RSA_padding_add_PKCS1_OAEP() and RSA_padding_check_PKCS1_OAEP() were added in OpenSSL 0.9.2b.