pkcs7_padding.h

#ifndef _PKCS7_PADDING_H_
#define _PKCS7_PADDING_H_

#include <stdint.h>
#include <stddef.h>

/* Pad a buffer with bytes as defined in PKCS#7 
 * Returns the number of pad bytes added, or zero if
 * the buffer size is not large enough to hold the correctly padded data
 */
int pkcs7_padding_pad_buffer( uint8_t *buffer,  size_t data_length, size_t buffer_size, uint8_t modulus );

int pkcs7_padding_valid( uint8_t *buffer, size_t data_length, size_t buffer_size, uint8_t modulus );

/* Given a block of pkcs7 padded data, return the actual data length in the block based on the padding applied.
 * buffer_size must be a multiple of modulus
 * last byte 'x' in buffer must be between 1 and modulus
 * buffer_size must be at least x + 1 in size
 * last 'x' bytes in buffer must be same as 'x'
 * returned size will be buffer_size - 'x'
 */
size_t pkcs7_padding_data_length( uint8_t * buffer, size_t buffer_size, uint8_t modulus );

#endif