RSA_PADDING_ADD_PKCS1_TYPE_1(3) | Library Functions Manual | RSA_PADDING_ADD_PKCS1_TYPE_1(3)

# NAME

`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_none`, `RSA_padding_check_none` — asymmetric encryption padding

# SYNOPSIS

library “libcrypto”
`#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_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);

# DESCRIPTION

These 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_*`() 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:

PKCS1_type_1
  PKCS #1 v2.0 EMSA-PKCS1-v1_5 (PKCS #1 v1.5 block type 1); used for signatures
PKCS1_type_2
  PKCS #1 v2.0 EME-PKCS1-v1_5 (PKCS #1 v1.5 block type 2)
PKCS1_OAEP
  PKCS #1 v2.0 EME-OAEP
none
  simply copy the data

`RSA_padding_check_*`() 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_*_OAEP`(), p points to the encoding parameter of length pl. p may be `NULL` if pl is 0.

# RETURN VALUES

The `RSA_padding_add_*`() functions return 1 on success or 0 on error. The `RSA_padding_check_*`() functions return the length of the recovered data or -1 on error. Error codes can be obtained by calling ERR_get_error(3).

# SEE ALSO

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

# HISTORY

`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_none`(), and `RSA_padding_check_none`() first appeared in SSLeay 0.9.0 and have been available since OpenBSD 2.4.

`RSA_padding_add_PKCS1_OAEP`() and `RSA_padding_check_PKCS1_OAEP`() first appeared in OpenSSL 0.9.2b and have been available since OpenBSD 2.6.

# BUGS

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.

June 8, 2025 | Debian