常见加密算法
常见的加密算法可以分成三类，对称加密算法，非对称加密算法和Hash算法。
Base64
BASE64并不能算为一种加密算法，而是一种编码方式，通常用于把二进制数据编码为可写的字符形式的数据。BASE64是一种可逆的编码方式。
它通常用作存储、传输一些二进制数据编码方法！也是MIME（多用途互联网邮件扩展，主要用作电子邮件标准）中一种可打印字符表示二进制数据的常见编码方法！
编码过程
- 首先将待编码的内容转换成8位二进制，每3个字符为一组；
- 如果编码前的长度是3n+1，编码后的内容最后面补上2个 ‘=’，如果编码前的长度是3n+2，编码后的内容最后面补上1个 ‘=’。
- 再将每一组的二进制内容拆分成6位的二进制，不足6位的后面补足0；
- 每个6进制的数字前面补足0，保证变成8位二进制；
- 将补足后的内容根据base64编码表转换成base64内容输出；
JAVA实现
/**
* 编码类
*/
public static class Encoder {
private final byte[] newline;
private final int linemax;
private final boolean isURL;
private final boolean doPadding;
private Encoder(boolean isURL, byte[] newline, int linemax, boolean doPadding) {
this.isURL = isURL;
this.newline = newline;
this.linemax = linemax;
this.doPadding = doPadding;
}
private static final char[] toBase64 = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
};
private static final char[] toBase64URL = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_'
}
private final int outLength(int srclen) {
int len = 0;
if (doPadding) {
len = 4 * ((srclen + 2) / 3);
} else {
int n = srclen % 3;
len = 4 * (srclen / 3) + (n == 0 ? 0 : n + 1);
}
if (linemax > 0) // line separators
len += (len - 1) / linemax * newline.length;
return len;
}
/**
* 编码
* @param src
* @return
*/
public byte[] encode(byte[] src) {
int len = outLength(src.length); // dst array size
byte[] dst = new byte[len];
int ret = encode0(src, 0, src.length, dst);
if (ret != dst.length)
return Arrays.copyOf(dst, ret);
return dst;
}
/**
* 编码
* @param src
* @return
*/
public String encodeToString(byte[] src) {
byte[] encoded = encode(src);
return new String(encoded, 0, encoded.length,StandardCharsets.UTF_8);
}
private int encode0(byte[] src, int off, int end, byte[] dst) {
char[] base64 = isURL ? toBase64URL : toBase64;
int sp = off;
int slen = (end - off) / 3 * 3;
int sl = off + slen;
if (linemax > 0 && slen > linemax / 4 * 3)
slen = linemax / 4 * 3;
int dp = 0;
while (sp < sl) {
int sl0 = Math.min(sp + slen, sl);
for (int sp0 = sp, dp0 = dp ; sp0 < sl0; ) {
int bits = (src[sp0++] & 0xff) << 16 |
(src[sp0++] & 0xff) << 8 |
(src[sp0++] & 0xff);
dst[dp0++] = (byte)base64[(bits >>> 18) & 0x3f];
dst[dp0++] = (byte)base64[(bits >>> 12) & 0x3f];
dst[dp0++] = (byte)base64[(bits >>> 6) & 0x3f];
dst[dp0++] = (byte)base64[bits & 0x3f];
}
int dlen = (sl0 - sp) / 3 * 4;
dp += dlen;
sp = sl0;
if (dlen == linemax && sp < end) {
for (byte b : newline){
dst[dp++] = b;
}
}
}
if (sp < end) { // 1 or 2 leftover bytes
int b0 = src[sp++] & 0xff;
dst[dp++] = (byte)base64[b0 >> 2];
if (sp == end) {
dst[dp++] = (byte)base64[(b0 << 4) & 0x3f];
if (doPadding) {
dst[dp++] = '=';
dst[dp++] = '=';
}
} else {
int b1 = src[sp++] & 0xff;
dst[dp++] = (byte)base64[(b0 << 4) & 0x3f | (b1 >> 4)];
dst[dp++] = (byte)base64[(b1 << 2) & 0x3f];
if (doPadding) {
dst[dp++] = '=';
}
}
}
return dp;
}
}
/**
* 解码类
*/
public static class Decoder {
private final boolean isURL;
private final boolean isMIME;
private Decoder(boolean isURL, boolean isMIME) {
this.isURL = isURL;
this.isMIME = isMIME;
}
private static final int[] fromBase64 = new int[256];
static {
Arrays.fill(fromBase64, -1);
for (int i = 0; i < Encoder.toBase64.length; i++)
fromBase64[Encoder.toBase64[i]] = i;
fromBase64['='] = -2;
}
private static final int[] fromBase64URL = new int[256];
static {
Arrays.fill(fromBase64URL, -1);
for (int i = 0; i < Encoder.toBase64URL.length; i++)
fromBase64URL[Encoder.toBase64URL[i]] = i;
fromBase64URL['='] = -2;
}
/**
* 解码
* @param src
* @return
*/
public byte[] decode(byte[] src) {
byte[] dst = new byte[outLength(src, 0, src.length)];
int ret = decode0(src, 0, src.length, dst);
if (ret != dst.length) {
dst = Arrays.copyOf(dst, ret);
}
return dst;
}
/**
* 解码
* @param src
* @return
*/
public byte[] decode(String src) {
return decode(src.getBytes(StandardCharsets.UTF_8));
}
private int outLength(byte[] src, int sp, int sl) {
int[] base64 = isURL ? fromBase64URL : fromBase64;
int paddings = 0;
int len = sl - sp;
if (len == 0)
return 0;
if (len < 2) {
if (isMIME && base64[0] == -1)
return 0;
throw new IllegalArgumentException(
"Input byte[] should at least have 2 bytes for base64 bytes");
}
if (isMIME) {
// scan all bytes to fill out all non-alphabet. a performance
// trade-off of pre-scan or Arrays.copyOf
int n = 0;
while (sp < sl) {
int b = src[sp++] & 0xff;
if (b == '=') {
len -= (sl - sp + 1);
break;
}
if ((b = base64[b]) == -1)
n++;
}
len -= n;
} else {
if (src[sl - 1] == '=') {
paddings++;
if (src[sl - 2] == '=')
paddings++;
}
}
if (paddings == 0 && (len & 0x3) != 0)
paddings = 4 - (len & 0x3);
return 3 * ((len + 3) / 4) - paddings;
}
private int decode0(byte[] src, int sp, int sl, byte[] dst) {
int[] base64 = isURL ? fromBase64URL : fromBase64;
int dp = 0;
int bits = 0;
int shiftto = 18; // pos of first byte of 4-byte atom
while (sp < sl) {
int b = src[sp++] & 0xff;
if ((b = base64[b]) < 0) {
if (b == -2) { // padding byte '='
// = shiftto==18 unnecessary padding
// x= shiftto==12 a dangling single x
// x to be handled together with non-padding case
// xx= shiftto==6&&sp==sl missing last =
// xx=y shiftto==6 last is not =
if (shiftto == 6 && (sp == sl || src[sp++] != '=') ||
shiftto == 18) {
throw new IllegalArgumentException(
"Input byte array has wrong 4-byte ending unit");
}
break;
}
if (isMIME) // skip if for rfc2045
continue;
else
throw new IllegalArgumentException(
"Illegal base64 character " +
Integer.toString(src[sp - 1], 16));
}
bits |= (b << shiftto);
shiftto -= 6;
if (shiftto < 0) {
dst[dp++] = (byte)(bits >> 16);
dst[dp++] = (byte)(bits >> 8);
dst[dp++] = (byte)(bits);
shiftto = 18;
bits = 0;
}
}
// reached end of byte array or hit padding '=' characters.
if (shiftto == 6) {
dst[dp++] = (byte)(bits >> 16);
} else if (shiftto == 0) {
dst[dp++] = (byte)(bits >> 16);
dst[dp++] = (byte)(bits >> 8);
} else if (shiftto == 12) {
// dangling single "x", incorrectly encoded.
throw new IllegalArgumentException(
"Last unit does not have enough valid bits");
}
// anything left is invalid, if is not MIME.
// if MIME, ignore all non-base64 character
while (sp < sl) {
if (isMIME && base64[src[sp++]] < 0)
continue;
throw new IllegalArgumentException(
"Input byte array has incorrect ending byte at " + sp);
}
return dp;
}
}
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