简单但不平凡的加密算法 - XXTEA

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#include <stdint.h>
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void encrypt (uint32_t* v, uint32_t* k) {
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    uint32_t v0=v[0], v1=v[1], sum=0, i;           /* set up */
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    uint32_t delta=0x9e3779b9;                     /* a key schedule constant */
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    uint32_t k0=k[0], k1=k[1], k2=k[2], k3=k[3];   /* cache key */
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    for (i=0; i < 32; i++) {                       /* basic cycle start */
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        sum += delta;
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        v0 += ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1);
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        v1 += ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3);
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    }                                              /* end cycle */
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    v[0]=v0; v[1]=v1;
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}
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void decrypt (uint32_t* v, uint32_t* k) {
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    uint32_t v0=v[0], v1=v[1], sum=0xC6EF3720, i;  /* set up */
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    uint32_t delta=0x9e3779b9;                     /* a key schedule constant */
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    uint32_t k0=k[0], k1=k[1], k2=k[2], k3=k[3];   /* cache key */
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    for (i=0; i<32; i++) {                         /* basic cycle start */
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        v1 -= ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3);
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        v0 -= ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1);
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        sum -= delta;
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    }                                              /* end cycle */
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    v[0]=v0; v[1]=v1;
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}

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/**
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* Convert byte array to int array.
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*/
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private static int[] toIntArray(byte[] data, boolean includeLength) {
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    int n = (((data.length & 3) == 0) ? (data.length >>> 2) : ((data.length >>> 2) + 1));
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    int[] result;
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    if (includeLength) {
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        result = new int[n + 1];
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        result[n] = data.length;
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    } else {
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        result = new int[n];
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    }
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    n = data.length;
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    for (int i = 0; i < n; i++) {
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        result[i >>> 2] |= (0x000000ff & data[i]) << ((i & 3) << 3);
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    }
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    return result;
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}

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/**
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* Encrypt data with key.
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*/
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public static int[] encrypt(int[] v, int[] k) {
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    int n = v.length - 1;
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    if (n < 1) {
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        return v;
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    }
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    if (k.length < 4) {
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        int[] key = new int[4];
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        System.arraycopy(k, 0, key, 0, k.length);
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        k = key;
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    }
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    int z = v[n], y = v[0], delta = 0x9E3779B9, sum = 0, e;
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    int p, q = 6 + 52 / (n + 1);
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    while (q-- > 0) {
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        sum = sum + delta;
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        e = sum >>> 2 & 3;
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        for (p = 0; p < n; p++) {
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            y = v[p + 1];
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            z = v[p] += (z >>> 5 ^ y << 2) + (y >>> 3 ^ z << 4) ^ (sum ^ y) + (k[p & 3 ^ e] ^ z);
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        }
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        y = v[0];
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        z = v[n] += (z >>> 5 ^ y << 2) + (y >>> 3 ^ z << 4) ^ (sum ^ y) + (k[p & 3 ^ e] ^ z);
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    }
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    return v;
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}

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/**
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* Decrypt data with key.
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*/
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public static int[] decrypt(int[] v, int[] k) {
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    int n = v.length - 1;
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    if (n < 1) {
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        return v;
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    }
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    if (k.length < 4) {
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        int[] key = new int[4];
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        System.arraycopy(k, 0, key, 0, k.length);
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        k = key;
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    }
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    int z = v[n], y = v[0], delta = 0x9E3779B9, sum, e;
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    int p, q = 6 + 52 / (n + 1);
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    sum = q * delta;
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    while (sum != 0) {
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        e = sum >>> 2 & 3;
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        for (p = n; p > 0; p--) {
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            z = v[p - 1];
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            y = v[p] -= (z >>> 5 ^ y << 2) + (y >>> 3 ^ z << 4) ^ (sum ^ y) + (k[p & 3 ^ e] ^ z);
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        }
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        z = v[n];
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        y = v[0] -= (z >>> 5 ^ y << 2) + (y >>> 3 ^ z << 4) ^ (sum ^ y) + (k[p & 3 ^ e] ^ z);
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        sum = sum - delta;
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    }
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    return v;
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}

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/**
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* Convert int array to byte array.
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*/
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private static byte[] toByteArray(int[] data, boolean includeLength) {
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    int n = data.length << 2;
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    if (includeLength) {
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        int m = data[data.length - 1];
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        if (m > n) {
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            return null;
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        } else {
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            n = m;
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        }
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    }
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    byte[] result = new byte[n];
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    for (int i = 0; i < n; i++) {
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        result[i] = (byte) ((data[i >>> 2] >>> ((i & 3) << 3)) & 0xff);
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    }
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    return result;
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}