Base64加密解密原理以及代码实现
转自:http://blog.csdn.net/jacky_dai/article/details/4698461
1. Base64使用A--Z,a--z,0--9,+,/ 这64个字符.
2. 编码原理:将3个字节转换成4个字节( (3 X 8) = 24 = (4 X 6) )先读入3个字节,每读一个字节,左移8位,再右移四次,每次6位,这样就有4个字节了.
3. 解码原理:将4个字节转换成3个字节.先读入4个6位(用或运算),每次左移6位,再右移3次,每次8位.这样就还原了.
Base64是一种很常见的编码规范,其作用是将二进制序列转换为人类可读的ASCII字符序列,常用在需用通过文本协议(比如HTTP和SMTP)来传输二进制数据的情况下。Base64并不是一种用于安全领域的加密解密算法(这类算法有DES等),尽管我们有时也听到使用Base64来加密解密的说法,但这里所说的加密与解密实际是指编码(encode)和解码(decode)的过程,其变换是非常简单的,仅仅能够避免信息被直接识别。
Base64采用了一种很简单的编码转换:对于待编码数据,以3个字节为单位,依次取6位数据并在前面补上两个0形成新的8位编码,由于3*8=4*6,这样3个字节的输入会变成4个字节的输出,长度上增加了1/3。
上面的处理还不能保证得到的字符都是可见字符,为了达到此目的,Base64制定了一个编码表,进行统一的转换。码表的大小为2^6=64,这也是Base64名称的由来。
Base64编码表
Value Encoding Value Encoding Value Encoding Value Encoding
0 A 17 R 34 i 51 z
1 B 18 S 35 j 52 0
2 C 19 T 36 k 53 1
3 D 20 U 37 l 54 2
4 E 21 V 38 m 55 3
5 F 22 W 39 n 56 4
6 G 23 X 40 o 57 5
7 H 24 Y 41 p 58 6
8 I 25 Z 42 q 59 7
9 J 26 a 43 r 60 8
10 K 27 b 44 s 61 9
11 L 28 c 45 t 62 +
12 M 29 d 46 u 63 /
13 N 30 e 47 v
14 O 31 f 48 w (pad) =
15 P 32 g 49 x
16 Q 33 h 50 y
Base64编解码算法都很简单,网上有很多源码,这里就不介绍了。
另外还有一点要注意的地方,前面提到编码是以3个字节为单位,当剩下的字符数量不足3个字节时,则应使用0进行填充,相应的,输出字符则使用‘=‘占位,因此编码后输出的文本末尾可能会出现1至2个‘=‘。
这是一种典型的编码转换的处理方法,类似的可能还有UTF16与UTF8之间的转换。
[cpp] view plaincopy
- /**
- * /file base64.h
- */
- #ifndef XYSSL_BASE64_H
- #define XYSSL_BASE64_H
- #define XYSSL_ERR_BASE64_BUFFER_TOO_SMALL -0x0010
- #define XYSSL_ERR_BASE64_INVALID_CHARACTER -0x0012
- #ifdef __cplusplus
- extern "C" {
- #endif
- /**
- * /brief Encode a buffer into base64 format
- *
- * /param dst destination buffer
- * /param dlen size of the buffer
- * /param src source buffer
- * /param slen amount of data to be encoded
- *
- * /return 0 if successful, or XYSSL_ERR_BASE64_BUFFER_TOO_SMALL.
- * *dlen is always updated to reflect the amount
- * of data that has (or would have) been written.
- *
- * /note Call this function with *dlen = 0 to obtain the
- * required buffer size in *dlen
- */
- int base64_encode(const unsigned char *src, int slen,unsigned char *dst, int *dlen);
- /**
- * /brief Decode a base64-formatted buffer
- *
- * /param dst destination buffer
- * /param dlen size of the buffer
- * /param src source buffer
- * /param slen amount of data to be decoded
- *
- * /return 0 if successful, XYSSL_ERR_BASE64_BUFFER_TOO_SMALL, or
- * XYSSL_ERR_BASE64_INVALID_DATA if the input data is not
- * correct. *dlen is always updated to reflect the amount
- * of data that has (or would have) been written.
- *
- * /note Call this function with *dlen = 0 to obtain the
- * required buffer size in *dlen
- */
- int base64_decode(const unsigned char *src, int slen,unsigned char *dst, int *dlen);
- /**
- * /brief Checkup routine
- *
- * /return 0 if successful, or 1 if the test failed
- */
- int base64_self_test( int verbose );
- #ifdef __cplusplus
- }
- #endif
- class CBase64
- {
- public:
- CBase64();
- virtual ~CBase64();
- static BOOL Encrypt(const unsigned char *pSrc,int iSlen,unsigned char *pDst,int *iDlen,CString &strErrorInfo);
- static BOOL Decrypt(const unsigned char *pSrc,int iSlen,unsigned char *pDst,int *iDlen,CString &strErrorInfo);
- private:
- };
- #endif /* base64.h */
[cpp] view plaincopy
- //source file: base64.cpp
- /*
- * RFC 1521 base64 encoding/decoding
- *
- * Copyright (C) 2006-2007 Christophe Devine
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License, version 2.1 as published by the Free Software Foundation.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
- * MA 02110-1301 USA
- */
- #include "stdafx.h"
- #include "base64.h"
- static const unsigned char base64_enc_map[64] =
- {
- ‘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‘, ‘+‘, ‘/‘
- };
- static const unsigned char base64_dec_map[128] =
- {
- 127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
- 127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
- 127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
- 127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
- 127, 127, 127, 62, 127, 127, 127, 63, 52, 53,
- 54, 55, 56, 57, 58, 59, 60, 61, 127, 127,
- 127, 64, 127, 127, 127, 0, 1, 2, 3, 4,
- 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
- 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
- 25, 127, 127, 127, 127, 127, 127, 26, 27, 28,
- 29, 30, 31, 32, 33, 34, 35, 36, 37, 38,
- 39, 40, 41, 42, 43, 44, 45, 46, 47, 48,
- 49, 50, 51, 127, 127, 127, 127, 127
- };
- /*
- * Encode a buffer into base64 format
- */
- int base64_encode(const unsigned char *src, int slen,unsigned char *dst, int *dlen)
- {
- int i, n;
- int C1, C2, C3;
- unsigned char *p;
- if( slen == 0 )
- return( 0 );
- n = (slen << 3) / 6;
- switch( (slen << 3) - (n * 6) )
- {
- case 2: n += 3; break;
- case 4: n += 2; break;
- default: break;
- }
- if( *dlen < n + 1 )
- {
- *dlen = n + 1;
- return( XYSSL_ERR_BASE64_BUFFER_TOO_SMALL );
- }
- n = (slen / 3) * 3;
- for( i = 0, p = dst; i < n; i += 3 )
- {
- C1 = *src++;
- C2 = *src++;
- C3 = *src++;
- *p++ = base64_enc_map[(C1 >> 2) & 0x3F];
- *p++ = base64_enc_map[(((C1 & 3) << 4) + (C2 >> 4)) & 0x3F];
- *p++ = base64_enc_map[(((C2 & 15) << 2) + (C3 >> 6)) & 0x3F];
- *p++ = base64_enc_map[C3 & 0x3F];
- }
- if( i < slen )
- {
- C1 = *src++;
- C2 = ((i + 1) < slen) ? *src++ : 0;
- *p++ = base64_enc_map[(C1 >> 2) & 0x3F];
- *p++ = base64_enc_map[(((C1 & 3) << 4) + (C2 >> 4)) & 0x3F];
- if( (i + 1) < slen )
- *p++ = base64_enc_map[((C2 & 15) << 2) & 0x3F];
- else *p++ = ‘=‘;
- *p++ = ‘=‘;
- }
- *dlen =static_cast<int>(p - dst);
- *p = 0;
- return( 0 );
- }
- /*
- * Decode a base64-formatted buffer
- */
- int base64_decode(const unsigned char *src, int slen,unsigned char *dst, int *dlen)
- {
- int i, j, n;
- unsigned long x;
- unsigned char *p;
- for( i = j = n = 0; i < slen; i++ )
- {
- if( ( slen - i ) >= 2 &&
- *(src+i) == ‘/r‘ && *(src+i+1) == ‘/n‘ )
- continue;
- if(*(src+i) == ‘/n‘ )
- continue;
- if(*(src+i) == ‘=‘ && ++j > 2 )
- return( XYSSL_ERR_BASE64_INVALID_CHARACTER );
- if(*(src+i) > 127 || base64_dec_map[*(src+i)] == 127 )
- return( XYSSL_ERR_BASE64_INVALID_CHARACTER );
- if( base64_dec_map[*(src+i)] < 64 && j != 0 )
- return( XYSSL_ERR_BASE64_INVALID_CHARACTER );
- n++;
- }
- if( n == 0 )
- return( 0 );
- n = ((n * 6) + 7) >> 3;
- if( *dlen < n )
- {
- *dlen = n;
- return( XYSSL_ERR_BASE64_BUFFER_TOO_SMALL );
- }
- for( j = 3, n = x = 0, p = dst; i > 0; i--, src++ )
- {
- if( *src == ‘/r‘ || *src == ‘/n‘ )
- continue;
- j -= ( base64_dec_map[*src] == 64 );
- x = (x << 6) | ( base64_dec_map[*src] & 0x3F );
- if( ++n == 4 )
- {
- n = 0;
- if( j > 0 ) *p++ = (unsigned char)( x >> 16 );
- if( j > 1 ) *p++ = (unsigned char)( x >> 8 );
- if( j > 2 ) *p++ = (unsigned char)( x );
- }
- }
- *dlen =static_cast<int>(p - dst);
- return( 0 );
- }
- BOOL CBase64::Encrypt(const unsigned char *pSrc,int iSlen,unsigned char *pDst,int *iDlen,CString &strErrorInfo)
- {
- strErrorInfo=_T("");
- int iRet=base64_encode(pSrc,iSlen,pDst,iDlen);
- if(iRet==XYSSL_ERR_BASE64_BUFFER_TOO_SMALL)
- strErrorInfo=_T("分配的缓冲区太小!");
- else if(iRet==XYSSL_ERR_BASE64_INVALID_CHARACTER)
- strErrorInfo=_T("无效数据!");
- return iRet==0;
- }
- BOOL CBase64::Decrypt(const unsigned char *pSrc,int iSlen,unsigned char *pDst,int *iDlen,CString &strErrorInfo)
- {
- strErrorInfo=_T("");
- int iRet=base64_decode(pSrc,iSlen,pDst,iDlen);
- if(iRet==XYSSL_ERR_BASE64_BUFFER_TOO_SMALL)
- strErrorInfo=_T("分配的缓冲区太小!");
- else if(iRet==XYSSL_ERR_BASE64_INVALID_CHARACTER)
- strErrorInfo=_T("无效数据!");
- return iRet==0;
- }