/* From Rosetta Code */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
typedef unsigned char ubyte;
 
#define KEY_LEN 8
typedef ubyte des_key_t[KEY_LEN];
 
const static ubyte PC1[] = {
    57, 49, 41, 33, 25, 17,  9,
     1, 58, 50, 42, 34, 26, 18,
    10,  2, 59, 51, 43, 35, 27,
    19, 11,  3, 60, 52, 44, 36,
    63, 55, 47, 39, 31, 23, 15,
     7, 62, 54, 46, 38, 30, 22,
    14,  6, 61, 53, 45, 37, 29,
    21, 13,  5, 28, 20, 12,  4
};
 
const static ubyte PC2[] = {
    14, 17, 11, 24,  1,  5,
     3, 28, 15,  6, 21, 10,
    23, 19, 12,  4, 26,  8,
    16,  7, 27, 20, 13,  2,
    41, 52, 31, 37, 47, 55,
    30, 40, 51, 45, 33, 48,
    44, 49, 39, 56, 34, 53,
    46, 42, 50, 36, 29, 32
};
 
const static ubyte IP[] = {
    58, 50, 42, 34, 26, 18, 10,  2,
    60, 52, 44, 36, 28, 20, 12,  4,
    62, 54, 46, 38, 30, 22, 14,  6,
    64, 56, 48, 40, 32, 24, 16,  8,
    57, 49, 41, 33, 25, 17,  9,  1,
    59, 51, 43, 35, 27, 19, 11,  3,
    61, 53, 45, 37, 29, 21, 13,  5,
    63, 55, 47, 39, 31, 23, 15,  7
};
 
const static ubyte E[] = {
    32,  1,  2,  3,  4,  5,
     4,  5,  6,  7,  8,  9,
     8,  9, 10, 11, 12, 13,
    12, 13, 14, 15, 16, 17,
    16, 17, 18, 19, 20, 21,
    20, 21, 22, 23, 24, 25,
    24, 25, 26, 27, 28, 29,
    28, 29, 30, 31, 32,  1
};
 
const static ubyte S[][64] = {
    {
        14,  4, 13,  1,  2, 15, 11,  8,  3, 10,  6, 12,  5,  9,  0,  7,
         0, 15,  7,  4, 14,  2, 13,  1, 10,  6, 12, 11,  9,  5,  3,  8,
         4,  1, 14,  8, 13,  6,  2, 11, 15, 12,  9,  7,  3, 10,  5,  0,
        15, 12,  8,  2,  4,  9,  1,  7,  5, 11,  3, 14, 10,  0,  6, 13
    },
    {
        15,  1,  8, 14,  6, 11,  3,  4,  9,  7,  2, 13, 12,  0,  5, 10,
         3, 13,  4,  7, 15,  2,  8, 14, 12,  0,  1, 10,  6,  9, 11,  5,
         0, 14,  7, 11, 10,  4, 13,  1,  5,  8, 12,  6,  9,  3,  2, 15,
        13,  8, 10,  1,  3, 15,  4,  2, 11,  6,  7, 12,  0,  5, 14,  9
    },
    {
        10,  0,  9, 14,  6,  3, 15,  5,  1, 13, 12,  7, 11,  4,  2,  8,
        13,  7,  0,  9,  3,  4,  6, 10,  2,  8,  5, 14, 12, 11, 15,  1,
        13,  6,  4,  9,  8, 15,  3,  0, 11,  1,  2, 12,  5, 10, 14,  7,
         1, 10, 13,  0,  6,  9,  8,  7,  4, 15, 14,  3, 11,  5,  2, 12
    },
    {
         7, 13, 14,  3,  0,  6,  9, 10,  1,  2,  8,  5, 11, 12,  4, 15,
        13,  8, 11,  5,  6, 15,  0,  3,  4,  7,  2, 12,  1, 10, 14,  9,
        10,  6,  9,  0, 12, 11,  7, 13, 15,  1,  3, 14,  5,  2,  8,  4,
         3, 15,  0,  6, 10,  1, 13,  8,  9,  4,  5, 11, 12,  7,  2, 14
    },
    {
         2, 12,  4,  1,  7, 10, 11,  6,  8,  5,  3, 15, 13,  0, 14,  9,
        14, 11,  2, 12,  4,  7, 13,  1,  5,  0, 15, 10,  3,  9,  8,  6,
         4,  2,  1, 11, 10, 13,  7,  8, 15,  9, 12,  5,  6,  3,  0, 14,
        11,  8, 12,  7,  1, 14,  2, 13,  6, 15,  0,  9, 10,  4,  5,  3
    },
    {
        12,  1, 10, 15,  9,  2,  6,  8,  0, 13,  3,  4, 14,  7,  5, 11,
        10, 15,  4,  2,  7, 12,  9,  5,  6,  1, 13, 14,  0, 11,  3,  8,
         9, 14, 15,  5,  2,  8, 12,  3,  7,  0,  4, 10,  1, 13, 11,  6,
         4,  3,  2, 12,  9,  5, 15, 10, 11, 14,  1,  7,  6,  0,  8, 13
    },
    {
         4, 11,  2, 14, 15,  0,  8, 13,  3, 12,  9,  7,  5, 10,  6,  1,
        13,  0, 11,  7,  4,  9,  1, 10, 14,  3,  5, 12,  2, 15,  8,  6,
         1,  4, 11, 13, 12,  3,  7, 14, 10, 15,  6,  8,  0,  5,  9,  2,
         6, 11, 13,  8,  1,  4, 10,  7,  9,  5,  0, 15, 14,  2,  3, 12
    },
    {
        13,  2,  8,  4,  6, 15, 11,  1, 10,  9,  3, 14,  5,  0, 12,  7,
         1, 15, 13,  8, 10,  3,  7,  4, 12,  5,  6, 11,  0, 14,  9,  2,
         7, 11,  4,  1,  9, 12, 14,  2,  0,  6, 10, 13, 15,  3,  5,  8,
         2,  1, 14,  7,  4, 10,  8, 13, 15, 12,  9,  0,  3,  5,  6, 11
    }
};
 
const static ubyte P[] = {
    16,  7, 20, 21,
    29, 12, 28, 17,
     1, 15, 23, 26,
     5, 18, 31, 10,
     2,  8, 24, 14,
    32, 27,  3,  9,
    19, 13, 30,  6,
    22, 11,  4, 25
};
 
const static ubyte IP2[] = {
    40,  8, 48, 16, 56, 24, 64, 32,
    39,  7, 47, 15, 55, 23, 63, 31,
    38,  6, 46, 14, 54, 22, 62, 30,
    37,  5, 45, 13, 53, 21, 61, 29,
    36,  4, 44, 12, 52, 20, 60, 28,
    35,  3, 43, 11, 51, 19, 59, 27,
    34,  2, 42, 10, 50, 18, 58, 26,
    33,  1, 41,  9, 49, 17, 57, 25
};
 
const static ubyte SHIFTS[] = {
    1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1
};
 
typedef struct {
    ubyte *data;
    int len;
} String;
 
/*
 * Transform a single nibble into a hex character
 *
 * in: a value < 0x10
 *
 * returns: the character that represents the nibble
 */
static char toHex(ubyte in) {
    if (0x00 <= in && in < 0x0A) {
        return '0' + in;
    }
    if (0x0A <= in && in <= 0x0F) {
        return 'A' + in - 0x0A;
    }
    return 0;
}
 
/*
 * Convert an array of bytes into a string
 *
 * ptr: the array of bytes
 * len: the number of bytes
 * out: a buffer allocated by the caller with enough space for 2*len+1 characters
 */
static void printBytes(const ubyte *ptr, int len, char *out) {
    while (len-- > 0) {
        *out++ = toHex(*ptr >> 4);
        *out++ = toHex(*ptr & 0x0F);
 
        ptr++;
    }
    *out = 0;
}
 
/*
 * Gets the value of a bit in an array of bytes
 *
 * src: the array of bytes to index
 * index: the desired bit to test the value of
 *
 * returns: the bit at the specified position in the array
 */
static int peekBit(const ubyte *src, int index) {
    int cell = index / 8;
    int bit = 7 - index % 8;
    return (src[cell] & (1 << bit)) != 0;
}
 
/*
 * Sets the value of a bit in an array of bytes
 *
 * dst: the array of bits to set a bit in
 * index: the position of the bit to set
 * value: the value for the bit to set
 */
static void pokeBit(ubyte *dst, int index, int value) {
    int cell = index / 8;
    int bit = 7 - index % 8;
    if (value == 0) {
        dst[cell] &= ~(1 << bit);
    } else {
        dst[cell] |= (1 << bit);
    }
}
 
/*
 * Transforms one array of bytes by shifting the bits the specified number of positions
 *
 * src: the array to shift bits from
 * len: the length of the src array
 * times: the number of positions that the bits should be shifted
 * dst: a bytes array allocated by the caller to store the shifted values
 */
static void shiftLeft(const ubyte *src, int len, int times, ubyte *dst) {
    int i, t;
    for (i = 0; i <= len; ++i) {
        pokeBit(dst, i, peekBit(src, i));
    }
    for (t = 1; t <= times; ++t) {
        int temp = peekBit(dst, 0);
        for (i = 1; i <= len; ++i) {
            pokeBit(dst, i - 1, peekBit(dst, i));
        }
        pokeBit(dst, len - 1, temp);
    }
}
 
/*
 * Calculates the sub keys to be used in processing the messages
 *
 * key: the array of bytes representing the key
 * ks: the subkeys that have been allocated by the caller
 */
typedef ubyte subdes_key_t[17][6]; /* 17 sets of 48 bits */
static void getSubKeys(const des_key_t key, subdes_key_t ks) {
    ubyte c[17][7];  /* 56 bits */
    ubyte d[17][4];  /* 28 bits */
    ubyte kp[7];
    int i, j;
 
    /* intialize */
    memset(c, 0, sizeof(c));
    memset(d, 0, sizeof(d));
    memset(ks, 0, sizeof(subdes_key_t));
 
    /* permute 'key' using table PC1 */
    for (i = 0; i < 56; ++i) {
        pokeBit(kp, i, peekBit(key, PC1[i] - 1));
    }
 
    /* split 'kp' in half and process the resulting series of 'c' and 'd' */
    for (i = 0; i < 28; ++i) {
        pokeBit(c[0], i, peekBit(kp, i));
        pokeBit(d[0], i, peekBit(kp, i + 28));
    }
 
    /* shift the components of c and d */
    for (i = 1; i < 17; ++i) {
        shiftLeft(c[i - 1], 28, SHIFTS[i - 1], c[i]);
        shiftLeft(d[i - 1], 28, SHIFTS[i - 1], d[i]);
    }
 
    /* merge 'd' into 'c' */
    for (i = 1; i < 17; ++i) {
        for (j = 28; j < 56; ++j) {
            pokeBit(c[i], j, peekBit(d[i], j - 28));
        }
    }
 
    /* form the sub-keys and store them in 'ks'
     * permute 'c' using table PC2 */
    for (i = 1; i < 17; ++i) {
        for (j = 0; j < 48; ++j) {
            pokeBit(ks[i], j, peekBit(c[i], PC2[j] - 1));
        }
    }
}
 
/*
 * Function used in processing the messages
 *
 * r: an array of bytes to be processed
 * ks: one of the subkeys to be used for processing
 * sp: output from the processing
 */
static void f(ubyte *r, ubyte *ks, ubyte *sp) {
    ubyte er[6]; /* 48 bits */
    ubyte sr[4]; /* 32 bits */
    int i;
 
    /* initialize */
    memset(er, 0, sizeof(er));
    memset(sr, 0, sizeof(sr));
 
    /* permute 'r' using table E */
    for (i = 0; i < 48; ++i) {
        pokeBit(er, i, peekBit(r, E[i] - 1));
    }
 
    /* xor 'er' with 'ks' and store back into 'er' */
    for (i = 0; i < 6; ++i) {
        er[i] ^= ks[i];
    }
 
    /* process 'er' six bits at a time and store resulting four bits in 'sr' */
    for (i = 0; i < 8; ++i) {
        int j = i * 6;
        int b[6];
        int k, row, col, m, n;
 
        for (k = 0; k < 6; ++k) {
            b[k] = peekBit(er, j + k) != 0 ? 1 : 0;
        }
 
        row = 2 * b[0] + b[5];
        col = 8 * b[1] + 4 * b[2] + 2 * b[3] + b[4];
        m = S[i][row * 16 + col]; /* apply table s */
        n = 1;
 
        while (m > 0) {
            int p = m % 2;
            pokeBit(sr, (i + 1) * 4 - n, p == 1);
            m /= 2;
            n++;
        }
    }
 
    /* permute sr using table P */
    for (i = 0; i < 32; ++i) {
        pokeBit(sp, i, peekBit(sr, P[i] - 1));
    }
}
 
/*
 * Processing of block of the message
 *
 * message: an 8 byte block from the message
 * ks: the subkeys to use in processing
 * ep: space for an encoded 8 byte block allocated by the caller
 */
static void processMessage(const ubyte *message, subdes_key_t ks, ubyte *ep) {
    ubyte left[17][4];  /* 32 bits */
    ubyte right[17][4]; /* 32 bits */
    ubyte mp[8];        /* 64 bits */
    ubyte e[8];         /* 64 bits */
    int i, j;
 
    /* permute 'message' using table IP */
    for (i = 0; i < 64; ++i) {
        pokeBit(mp, i, peekBit(message, IP[i] - 1));
    }
 
    /* split 'mp' in half and process the resulting series of 'l' and 'r */
    for (i = 0; i < 32; ++i) {
        pokeBit(left[0], i, peekBit(mp, i));
        pokeBit(right[0], i, peekBit(mp, i + 32));
    }
    for (i = 1; i < 17; ++i) {
        ubyte fs[4]; /* 32 bits */
 
        memcpy(left[i], right[i - 1], 4);
        f(right[i - 1], ks[i], fs);
        for (j = 0; j < 4; ++j) {
            left[i - 1][j] ^= fs[j];
        }
        memcpy(right[i], left[i - 1], 4);
    }
 
    /* amalgamate r[16] and l[16] (in that order) into 'e' */
    for (i = 0; i < 32; ++i) {
        pokeBit(e, i, peekBit(right[16], i));
    }
    for (i = 32; i < 64; ++i) {
        pokeBit(e, i, peekBit(left[16], i - 32));
    }
 
    /* permute 'e' using table IP2 ad return result as a hex string */
    for (i = 0; i < 64; ++i) {
        pokeBit(ep, i, peekBit(e, IP2[i] - 1));
    }
}
 
/*
 * Encrypts a message using DES
 *
 * key: the key to use to encrypt the message
 * message: the message to be encrypted
 * len: the length of the message
 *
 * returns: a paring of dynamically allocated memory for the encoded message,
 *          and the length of the encoded message.
 *          the caller will need to free the memory after use.
 */
String encrypt(const des_key_t key, const ubyte *message, int len) {
    String result = { 0, 0 };
    subdes_key_t ks;
    ubyte padByte;
    int i;
 
    getSubKeys(key, ks);
 
    padByte = 8 - len % 8;
    result.len = len + padByte;
    result.data = (ubyte*)malloc(result.len);
    memcpy(result.data, message, len);
    memset(&result.data[len], padByte, padByte);
 
    for (i = 0; i < result.len; i += 8) {
        processMessage(&result.data[i], ks, &result.data[i]);
    }
 
    return result;
}
 
/*
 * Decrypts a message using DES
 *
 * key: the key to use to decrypt the message
 * message: the message to be decrypted
 * len: the length of the message
 *
 * returns: a paring of dynamically allocated memory for the decoded message,
 *          and the length of the decoded message.
 *          the caller will need to free the memory after use.
 */
String decrypt(const des_key_t key, const ubyte *message, int len) {
    String result = { 0, 0 };
    subdes_key_t ks;
    int i, j;
    ubyte padByte;
 
    getSubKeys(key, ks);
    /* reverse the subkeys */
    for (i = 1; i < 9; ++i) {
        for (j = 0; j < 6; ++j) {
            ubyte temp = ks[i][j];
            ks[i][j] = ks[17 - i][j];
            ks[17 - i][j] = temp;
        }
    }
 
    result.data = (ubyte*)malloc(len);
    memcpy(result.data, message, len);
    result.len = len;
    for (i = 0; i < result.len; i += 8) {
        processMessage(&result.data[i], ks, &result.data[i]);
    }
 
    padByte = result.data[len - 1];
    result.len -= padByte;
    return result;
}
 
/*
 * Convienience method for showing the round trip processing of a message
 */
void driver(const des_key_t key, const ubyte *message, int len) {
    String encoded, decoded;
    char buffer[128];
 
    printBytes(key, KEY_LEN, buffer);
    printf("Key     : %s\n", buffer);
 
    printBytes(message, len, buffer);
    printf("Message : %s\n", buffer);
 
    encoded = encrypt(key, message, len);
    printBytes(encoded.data, encoded.len, buffer);
    printf("Encoded : %s\n", buffer);
 
    decoded = decrypt(key, encoded.data, encoded.len);
    printBytes(decoded.data, decoded.len, buffer);
    printf("Decoded : %s\n\n", buffer);
 
    /* release allocated memory */
    if (encoded.len > 0) {
        free(encoded.data);
        encoded.data = 0;
    }
    if (decoded.len > 0) {
        free(decoded.data);
        decoded.data = 0;
    }
}
 
int main() {
    const des_key_t keys[] = {
        {0x13, 0x34, 0x57, 0x79, 0x9B, 0xBC, 0xDF, 0xF1},
        {0x0E, 0x32, 0x92, 0x32, 0xEA, 0x6D, 0x0D, 0x73},
        {0x0E, 0x32, 0x92, 0x32, 0xEA, 0x6D, 0x0D, 0x73}
    };
    const ubyte message1[] = { 0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF };
    const ubyte message2[] = { 0x87, 0x87, 0x87, 0x87, 0x87, 0x87, 0x87, 0x87 };
    const ubyte message3[] = { 0x59, 0x6F, 0x75, 0x72, 0x20, 0x6C, 0x69, 0x70, 0x73, 0x20, 0x61, 0x72, 0x65, 0x20, 0x73, 0x6D, 0x6F, 0x6F, 0x74, 0x68, 0x65, 0x72, 0x20, 0x74, 0x68, 0x61, 0x6E, 0x20, 0x76, 0x61, 0x73, 0x65, 0x6C, 0x69, 0x6E, 0x65, 0x0D, 0x0A };
    int len;
 
    len = sizeof(message1) / sizeof(ubyte);
    driver(keys[0], message1, len);
 
    len = sizeof(message2) / sizeof(ubyte);
    driver(keys[1], message2, len);
 
    len = sizeof(message3) / sizeof(ubyte);
    driver(keys[2], message3, len);
}