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Set up C project for working on Cryptopals challenges
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‎.gitignore‎

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*.pyc
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*~
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*node_modules*
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*.dSYM
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*.out

‎Cryptopal-Challenges/brice/Makefile‎

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# For OSX, Install openssl with `brew install openssl`
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DEBUG=false
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CC=gcc
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LIBS= -lssl -lcrypto
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INCLUDES= -I/usr/local/opt/openssl/include
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LDFLAGS= -L/usr/local/opt/openssl/lib
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ifeq ($(DEBUG),true)
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CFLAGS="-g -O0"
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else
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CFLAGS=""
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endif
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main:
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$(CC) $(CFLAGS) src/try.c src/utils.c -o try.out -I./src/ $(LIBS) $(LDFLAGS) $(INCLUDES)

‎Cryptopal-Challenges/brice/Notes.md‎

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TODO
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====
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- [ ] Handle ecb mode with partial plaintext blocks gracefully

‎Cryptopal-Challenges/brice/api.h‎

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#include "common.h"
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/*
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* Block cipher modes of operation
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*/
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Mode MODE_ECB(void);
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Mode MODE_CBC(void);
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/*
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* Available ciphers
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*/
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Cipher AES_128_128(void);
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/*
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* Available padding modes
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*/
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Padding PKCS7(void);
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typedef ERROR (ENCRYPT_FN)(
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const unsigned char* plaintext,
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const int plaintext_length,
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OUT unsigned char* ciphertext,
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const int ciphertext_limit,
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OUT int* encrypted_bytes
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);
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typedef ERROR (DECRYPT_FN)(
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const unsigned char* ciphertext,
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const int ciphertext_length,
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OUT unsigned char* plaintext,
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const int plaintext_limit,
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OUT int* decrypted_bytes
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);
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typedef struct {
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unsigned char* key;
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unsigned char* iv;
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ENCRYPT_FN* encrypt;
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DECRYPT_FN* decrypt;
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} Cipher;
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Cipher CipherInit(
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Mode mode,
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Primitive cipher,
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Padding padding_mode,
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const unsigned char* key,
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const unsigned char* iv
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);
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const unsigned char* error_string(ERROR);
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void log_error(ERROR);

‎Cryptopal-Challenges/brice/src/common.h‎

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#define OUT /**/
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typedef enum {
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OK,
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IV_PROVIDED_IN_ERROR,
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LIMIT_TOO_SMALL,
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UNKNOWN_FATAL
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} ERROR;
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typedef ERROR (ENCRYPT_BLOCK)(
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const unsigned char* key,
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const unsigned char* plainblock,
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OUT unsigned char* cipherblock
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);
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typedef ERROR (DECRYPT_BLOCK)(
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const unsigned char* key,
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const unsigned char* cipherblock,
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OUT unsigned char* plainblock
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);
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typedef ERROR (PAD_FN)(
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const int block_size,
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const int text_length, /*The length of the text to be padded*/
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unsigned char* text, /* Pointer to the text buffer, which should be allocated as a multiple of block_size */
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const int text_limit
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);
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typedef ERROR (DEPAD_FN)(
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const int block_size,
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unsigned char* text, /* Pointer to the text buffer, We're going to 'depad' by overwriting the padding with '\0' */
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const int text_limit
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);
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typedef struct {
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int block_size;
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int key_size;
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ENCRYPT_BLOCK* encrypt;
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DECRYPT_BLOCK* decrypt;
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} Primitive;
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typedef struct {
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PAD_FN* pad;
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DEPAD_FN* depad;
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} Padding;
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typedef ERROR (MODE_ENCRYPT)(
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const Primitive* cipher,
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const Padding* padding,
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const unsigned char* key,
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const unsigned char* iv,
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const unsigned char* plaintext,
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const int plaintext_length,
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OUT unsigned char* ciphertext,
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const int ciphertext_limit
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);
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typedef ERROR (MODE_DECRYPT)(
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const Primitive* cipher,
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const Padding* padding,
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const unsigned char* key,
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const unsigned char* iv,
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const unsigned char* ciphertext,
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const int ciphertext_length,
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OUT unsigned char* plaintext,
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const int plaintext_limit
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);
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typedef struct {
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MODE_ENCRYPT* encrypt;
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MODE_DECRYPT* decrypt;
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} Mode;

‎Cryptopal-Challenges/brice/src/main.c‎

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#include <stdlib.h>
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#include "common.h"
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int main(){
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ERROR status = OK;
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/* For example: */
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Cipher AES_ECB = CipherInit(
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MODE_ECB(),
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RIJNDAEL_128_128(),
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PKCS7(),
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"YELLOW SUBMARINE",
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"I AM AN INIT VEC"
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);
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unsigned char original[] = "My big secret";
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int original_length = strlen(original);
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int ciphertext_limit = 64;
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unsigned char ciphertext[ciphertext_limit];
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int encrypted_bytes = 0;
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if(OK != (status = AES_ECB.encrypt(original, original_length, ciphertext, ciphertext_limit, &encrypted_bytes))){
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log_error(status);
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exit(1);
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};
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int plaintext_limit = 64;
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unsigned char plaintext[plaintext_limit];
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int decrypted_bytes = 0;
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if(OK != (status = AES_ECB.decrypt(ciphertext, encrypted_bytes, plaintext, plaintext_limit, &decrypted_bytes))){
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log_error(status);
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exit(1);
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};
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printf("ORIGINAL: ");print_hex(original);printf("\n");
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printf("CIPHERTEXT: ");print_hex(ciphertext);printf("\n");
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printf("PLAINTEXT: ");print_hex(plaintext);printf("\n");
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}

‎Cryptopal-Challenges/brice/src/try.c‎

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/*
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* Implement CBC mode
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*
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* CBC mode is a block cipher mode that allows us to encrypt
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* irregularly-sized messages, despite the fact that a block
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* cipher natively only transforms individual blocks.
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*
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* In CBC mode, each ciphertext block is added to the next
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* plaintext block before the next call to the cipher core.
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*
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* The first plaintext block, which has no associated previous
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* ciphertext block, is added to a "fake 0th ciphertext block"
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* called the initialization vector, or IV.
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*
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* Implement CBC mode by hand by taking the ECB function you
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* wrote earlier, making it encrypt instead of decrypt (verify
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* this by decrypting whatever you encrypt to test), and using
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* your XOR function from the previous exercise to combine them.
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*
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* The file here is intelligible (somewhat) when CBC decrypted
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* against "YELLOW SUBMARINE" with an IV of all ASCII 0
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* (\x00\x00\x00 &c)
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*/
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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#include <openssl/conf.h>
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#include <openssl/evp.h>
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#include <openssl/err.h>
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#include "utils.h"
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#include "common.h"
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static const int NO_PADDING = 0;
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static const int BLOCK_SIZE = 16;
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void handleErrors(void){
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ERR_print_errors_fp(stderr);
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abort();
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}
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void aes_encrypt_block(const unsigned char* plaintext, const unsigned char* key, unsigned char* ciphertext){
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EVP_CIPHER_CTX *ctx;
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int outlen, tmplen;
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// Create and initialise the context
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if(!(ctx = EVP_CIPHER_CTX_new())){
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handleErrors();
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}
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// Initialises context with cipher
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if(1 != EVP_EncryptInit_ex(ctx, EVP_aes_128_ecb(), NULL, key, NULL)){
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handleErrors();
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}
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// Don't PCKS5 pad
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EVP_CIPHER_CTX_set_padding(ctx, NO_PADDING);
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// Encrypt plaintext
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if(1 != EVP_EncryptUpdate(ctx, ciphertext, &outlen , plaintext, BLOCK_SIZE)){
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handleErrors();
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}
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// Finalise the encryption.
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if(1 != EVP_EncryptFinal_ex(ctx, ciphertext + outlen, &tmplen)){
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handleErrors();
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}
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// Clean up
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EVP_CIPHER_CTX_free(ctx);
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}
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void aes_decrypt_block(const unsigned char* ciphertext, const unsigned char* key, unsigned char* plaintext){
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EVP_CIPHER_CTX *ctx;
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int outlen, tmplen;
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// Create and initialise the context
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if(!(ctx = EVP_CIPHER_CTX_new())){
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handleErrors();
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}
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// Initialises context with cipher
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if(1 != EVP_DecryptInit_ex(ctx, EVP_aes_128_ecb(), NULL, key, NULL)){
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handleErrors();
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}
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// Don't PCKS5 pad
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EVP_CIPHER_CTX_set_padding(ctx, NO_PADDING);
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// Encrypt plaintext
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if(1 != EVP_DecryptUpdate(ctx, plaintext, &outlen , ciphertext, BLOCK_SIZE)){
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handleErrors();
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}
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// Finalise the encryption.
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if(1 != EVP_DecryptFinal_ex(ctx, plaintext + outlen, &tmplen)){
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handleErrors();
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}
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// Clean up
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EVP_CIPHER_CTX_free(ctx);
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}
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void test_basic_block_encryption(){
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unsigned char original[] = "TO BE OR NOT TO ";
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unsigned char key[] = "YELLOW SUBMARINE";
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unsigned char ciphertext[64];
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unsigned char plaintext[64];
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memset(ciphertext, 0, 64);
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memset(plaintext, 0, 64);
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printf("ORIGINAL: >%s<\n", original);
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printf("ORIGINAL: ");print_hex(original);printf("\n");
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aes_encrypt_block(original, key, ciphertext);
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aes_decrypt_block(ciphertext, key, plaintext);
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printf("CIPHERTEXT: ");print_hex(ciphertext);printf("\n");
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printf("PLAINTEXT: ");print_hex(plaintext);printf("\n");
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printf("PLAINTEXT: >%s<\n", plaintext);
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}
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void decrypt_ecb(
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const unsigned char* ciphertext,
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const unsigned char* key,
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const int len,
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unsigned char* plaintext
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){
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for( int offset = 0; offset < len; offset+=BLOCK_SIZE){
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aes_decrypt_block(ciphertext+offset, key, plaintext+offset);
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}
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}
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int main (int argc, char** agrv){
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// test_basic_block_encryption();
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unsigned char * ciphertext = NULL;
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long length = read_to_buffer("aes-test.dat", &ciphertext);
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if (!ciphertext){
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printf("No ciphertext found!\n");
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return 1;
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}
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unsigned char* plaintext = calloc(length, sizeof(unsigned char)+BLOCK_SIZE+BLOCK_SIZE);
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if(!plaintext){
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printf("Calloc returned null for some reason o_O?\n");
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free(ciphertext);
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return 1;
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}
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decrypt_ecb(ciphertext, (unsigned char *)"YELLOW SUBMARINE", length, plaintext);
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printf(">>%s\n", plaintext);
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free(plaintext);
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free(ciphertext);
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return 0;
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}

‎Cryptopal-Challenges/brice/src/utils.c‎

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#include <stdio.h>
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#include <stdlib.h>
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#include "utils.h"
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void print_hex(const unsigned char *s){
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while(*s)
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printf("%02x ", (unsigned int) *s++);
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}
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long read_to_buffer(const char* filename, unsigned char** buffer){
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long length = 0;
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FILE * f = fopen (filename, "rb");
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if (f){
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fseek (f, 0, SEEK_END);
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length = ftell (f);
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fseek (f, 0, SEEK_SET);
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*buffer = malloc (length);
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if (*buffer)
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{
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fread (*buffer, 1, length, f);
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}
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fclose (f);
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}
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return length;
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}

‎Cryptopal-Challenges/brice/src/utils.h‎

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void print_hex(const unsigned char *s);
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long read_to_buffer(const char* filename, unsigned char** buffer);

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