MD5哈希值也是一个很有用的。通常来做校验或者随机数或者是唯一ID。
在以前做的项目中也使用过。下面是MD5算法的J2ME版：
public class MD5Digest {
private static final int DIGEST_LENGTH = 16;
private static final int BYTE_LENGTH = 64;
private byte[] xBuf;
private int xBufOff;
private long byteCount;
private int H1, H2, H3, H4; // IV's
private int[] X = new int[16];
private int xOff;
public MD5Digest() {
xBuf = new byte[4];
xBufOff = 0;
reset();
}
public MD5Digest(final MD5Digest t) {
xBuf = new byte[t.xBuf.length];
System.arraycopy(t.xBuf, 0, xBuf, 0, t.xBuf.length);
xBufOff = t.xBufOff;
byteCount = t.byteCount;
H1 = t.H1;
H2 = t.H2;
H3 = t.H3;
H4 = t.H4;
System.arraycopy(t.X, 0, X, 0, t.X.length);
xOff = t.xOff;
}
public int doFinal(final byte[] out, final int outOff) {
finish();
unpackWord(H1, out, outOff);
unpackWord(H2, out, outOff + 4);
unpackWord(H3, out, outOff + 8);
unpackWord(H4, out, outOff + 12);
reset();
return DIGEST_LENGTH;
}
/**
* reset the chaining variables to the IV values.
*/
public void reset() {
byteCount = 0;
xBufOff = 0;
for (int i = 0; i < xBuf.length; i++) {
xBuf[i] = 0;
}
H1 = 0x67452301;
H2 = 0xefcdab89;
H3 = 0x98badcfe;
H4 = 0x10325476;
xOff = 0;
for (int i = 0; i != X.length; i++) {
X[i] = 0;
}
}
public void update(final byte in) {
xBuf[xBufOff++] = in;
if (xBufOff == xBuf.length) {
processWord(xBuf, 0);
xBufOff = 0;
}
byteCount++;
}
public void update(final byte[] in, int inOff, int len) {
//
// fill the current word
//
while ((xBufOff != 0) && (len > 0)) {
update(in[inOff]);
inOff++;
len--;
}
//
// process whole words.
//
while (len > xBuf.length) {
processWord(in, inOff);
inOff += xBuf.length;
len -= xBuf.length;
byteCount += xBuf.length;
}
//
// load in the remainder.
//
while (len > 0) {
update(in[inOff]);
inOff++;
len--;
}
}
public void finish() {
long bitLength = (byteCount << 3);
//
// add the pad bytes.
//
update((byte) 128);
while (xBufOff != 0) {
update((byte) 0);
}
processLength(bitLength);
processBlock();
}
public int getByteLength() {
return BYTE_LENGTH;
}
private void processWord(final byte[] in, final int inOff) {
X[xOff++] = (in[inOff] & 0xff) | ((in[inOff + 1] & 0xff) << 8)
| ((in[inOff + 2] & 0xff) << 16) |
((in[inOff + 3] & 0xff) << 24);
if (xOff == 16) {
processBlock();
}
}
private void processLength(final long bitLength) {
if (xOff > 14) {
processBlock();
}
//noinspection PointlessBitwiseExpression
X[14] = (int) (bitLength & 0xffffffff);
X[15] = (int) (bitLength >>> 32);
}
private void unpackWord(final int word, final byte[] out, final int outOff) {
out[outOff] = (byte) word;
out[outOff + 1] = (byte) (word >>> 8);
out[outOff + 2] = (byte) (word >>> 16);
out[outOff + 3] = (byte) (word >>> 24);
}
//
// round 1 left rotates
//
private static final int S11 = 7;
private static final int S12 = 12;
private static final int S13 = 17;
private static final int S14 = 22;
//
// round 2 left rotates
//
private static final int S21 = 5;
private static final int S22 = 9;
private static final int S23 = 14;
private static final int S24 = 20;
//
// round 3 left rotates
//
private static final int S31 = 4;
private static final int S32 = 11;
private static final int S33 = 16;
private static final int S34 = 23;
//
// round 4 left rotates
//
private static final int S41 = 6;
private static final int S42 = 10;
private static final int S43 = 15;
private static final int S44 = 21;
/*
* rotate int x left n bits.
*/
private int rotateLeft(final int x, final int n) {
return (x << n) | (x >>> (32 - n));
}
/*
* F, G, H and I are the basic MD5 functions.
*/
private int F(final int u, final int v, final int w) {
return (u & v) | (~u & w);
}
private int G(final int u, final int v, final int w) {
return (u & w) | (v & ~w);
}
private int H(final int u, final int v, final int w) {
return u ^ v ^ w;
}
private int K(final int u, final int v, final int w) {
return v ^ (u | ~w);
}
private void processBlock() {
int a = H1;
int b = H2;
int c = H3;
int d = H4;
//
// Round 1 - F cycle, 16 times.
//
a = rotateLeft(a + F(b, c, d) + X[0] + 0xd76aa478, S11) + b;
d = rotateLeft(d + F(a, b, c) + X[1] + 0xe8c7b756, S12) + a;
c = rotateLeft(c + F(d, a, b) + X[2] + 0x242070db, S13) + d;
b = rotateLeft(b + F(c, d, a) + X[3] + 0xc1bdceee, S14) + c;
a = rotateLeft(a + F(b, c, d) + X[4] + 0xf57c0faf, S11) + b;
d = rotateLeft(d + F(a, b, c) + X[5] + 0x4787c62a, S12) + a;
c = rotateLeft(c + F(d, a, b) + X[6] + 0xa8304613, S13) + d;
b = rotateLeft(b + F(c, d, a) + X[7] + 0xfd469501, S14) + c;
a = rotateLeft(a + F(b, c, d) + X[8] + 0x698098d8, S11) + b;
d = rotateLeft(d + F(a, b, c) + X[9] + 0x8b44f7af, S12) + a;
c = rotateLeft(c + F(d, a, b) + X[10] + 0xffff5bb1, S13) + d;
b = rotateLeft(b + F(c, d, a) + X[11] + 0x895cd7be, S14) + c;
a = rotateLeft(a + F(b, c, d) + X[12] + 0x6b901122, S11) + b;
d = rotateLeft(d + F(a, b, c) + X[13] + 0xfd987193, S12) + a;
c = rotateLeft(c + F(d, a, b) + X[14] + 0xa679438e, S13) + d;
b = rotateLeft(b + F(c, d, a) + X[15] + 0x49b40821, S14) + c;
//
// Round 2 - G cycle, 16 times.
//
a = rotateLeft(a + G(b, c, d) + X[1] + 0xf61e2562, S21) + b;
d = rotateLeft(d + G(a, b, c) + X[6] + 0xc040b340, S22) + a;
c = rotateLeft(c + G(d, a, b) + X[11] + 0x265e5a51, S23) + d;
b = rotateLeft(b + G(c, d, a) + X[0] + 0xe9b6c7aa, S24) + c;
a = rotateLeft(a + G(b, c, d) + X[5] + 0xd62f105d, S21) + b;
d = rotateLeft(d + G(a, b, c) + X[10] + 0x02441453, S22) + a;
c = rotateLeft(c + G(d, a, b) + X[15] + 0xd8a1e681, S23) + d;
b = rotateLeft(b + G(c, d, a) + X[4] + 0xe7d3fbc8, S24) + c;
a = rotateLeft(a + G(b, c, d) + X[9] + 0x21e1cde6, S21) + b;
d = rotateLeft(d + G(a, b, c) + X[14] + 0xc33707d6, S22) + a;
c = rotateLeft(c + G(d, a, b) + X[3] + 0xf4d50d87, S23) + d;
b = rotateLeft(b + G(c, d, a) + X[8] + 0x455a14ed, S24) + c;
a = rotateLeft(a + G(b, c, d) + X[13] + 0xa9e3e905, S21) + b;
d = rotateLeft(d + G(a, b, c) + X[2] + 0xfcefa3f8, S22) + a;
c = rotateLeft(c + G(d, a, b) + X[7] + 0x676f02d9, S23) + d;
b = rotateLeft(b + G(c, d, a) + X[12] + 0x8d2a4c8a, S24) + c;
//
// Round 3 - H cycle, 16 times.
//
a = rotateLeft(a + H(b, c, d) + X[5] + 0xfffa3942, S31) + b;
d = rotateLeft(d + H(a, b, c) + X[8] + 0x8771f681, S32) + a;
c = rotateLeft(c + H(d, a, b) + X[11] + 0x6d9d6122, S33) + d;
b = rotateLeft(b + H(c, d, a) + X[14] + 0xfde5380c, S34) + c;
a = rotateLeft(a + H(b, c, d) + X[1] + 0xa4beea44, S31) + b;
d = rotateLeft(d + H(a, b, c) + X[4] + 0x4bdecfa9, S32) + a;
c = rotateLeft(c + H(d, a, b) + X[7] + 0xf6bb4b60, S33) + d;
b = rotateLeft(b + H(c, d, a) + X[10] + 0xbebfbc70, S34) + c;
a = rotateLeft(a + H(b, c, d) + X[13] + 0x289b7ec6, S31) + b;
d = rotateLeft(d + H(a, b, c) + X[0] + 0xeaa127fa, S32) + a;
c = rotateLeft(c + H(d, a, b) + X[3] + 0xd4ef3085, S33) + d;
b = rotateLeft(b + H(c, d, a) + X[6] + 0x04881d05, S34) + c;
a = rotateLeft(a + H(b, c, d) + X[9] + 0xd9d4d039, S31) + b;
d = rotateLeft(d + H(a, b, c) + X[12] + 0xe6db99e5, S32) + a;
c = rotateLeft(c + H(d, a, b) + X[15] + 0x1fa27cf8, S33) + d;
b = rotateLeft(b + H(c, d, a) + X[2] + 0xc4ac5665, S34) + c;
//
// Round 4 - K cycle, 16 times.
//
a = rotateLeft(a + K(b, c, d) + X[0] + 0xf4292244, S41) + b;
d = rotateLeft(d + K(a, b, c) + X[7] + 0x432aff97, S42) + a;
c = rotateLeft(c + K(d, a, b) + X[14] + 0xab9423a7, S43) + d;
b = rotateLeft(b + K(c, d, a) + X[5] + 0xfc93a039, S44) + c;
a = rotateLeft(a + K(b, c, d) + X[12] + 0x655b59c3, S41) + b;
d = rotateLeft(d + K(a, b, c) + X[3] + 0x8f0ccc92, S42) + a;
c = rotateLeft(c + K(d, a, b) + X[10] + 0xffeff47d, S43) + d;
b = rotateLeft(b + K(c, d, a) + X[1] + 0x85845dd1, S44) + c;
a = rotateLeft(a + K(b, c, d) + X[8] + 0x6fa87e4f, S41) + b;
d = rotateLeft(d + K(a, b, c) + X[15] + 0xfe2ce6e0, S42) + a;
c = rotateLeft(c + K(d, a, b) + X[6] + 0xa3014314, S43) + d;
b = rotateLeft(b + K(c, d, a) + X[13] + 0x4e0811a1, S44) + c;
a = rotateLeft(a + K(b, c, d) + X[4] + 0xf7537e82, S41) + b;
d = rotateLeft(d + K(a, b, c) + X[11] + 0xbd3af235, S42) + a;
c = rotateLeft(c + K(d, a, b) + X[2] + 0x2ad7d2bb, S43) + d;
b = rotateLeft(b + K(c, d, a) + X[9] + 0xeb86d391, S44) + c;
H1 += a;
H2 += b;
H3 += c;
H4 += d;
//
// reset the offset and clean out the word buffer.
//
xOff = 0;
for (int i = 0; i != X.length; i++) {
X[i] = 0;
}
}
}