安全哈希算法（Secure Hash Algorithm）主要適用於數字簽名標准 （Digital Signature Standard DSS）裡面定義的數字簽名算法（Digital Signature Algorithm DSA）。對於長度小於2^64位的消息，SHA1會產生一個160位的消息摘要。當接收到消息的時候，這個消息摘要可以用來驗證數據的完整性。在傳輸的過程中，數據很可能會發生變化，那麼這時候就會產生不同的消息摘要。 SHA1有如下特性：不可以從消息摘要中復原信息；兩個不同的消息不會產生同樣的消息摘要。
將C語言梳理一下，分布在以下10個章節中：
C++ Primer Plus 第6版 中文版 清晰有書簽PDF+源代碼 http://www.linuxidc.com/Linux/2014-05/101227.htm
------------------------------------------源碼下載：------------------------------------------
免費下載地址在 http://linux.linuxidc.com/
用戶名與密碼都是www.linuxidc.com
具體下載目錄在 /2014年資料/6月/26日/C語言獲取文件的SHA1哈希值
下載方法見 http://www.linuxidc.com/Linux/2013-07/87684.htm
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SHA1 C語言實現
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <errno.h>
#undef BIG_ENDIAN_HOST
typedef unsigned int u32;
/****************
* Rotate a 32 bit integer by n bytes
*/
#if defined(__GNUC__) && defined(__i386__)
static inline u32
rol( u32 x, int n)
{
__asm__("roll %%cl,%0"
:"=r" (x)
:"0" (x),"c" (n));
return x;
}
#else
#define rol(x,n) ( ((x) << (n)) | ((x) >> (32-(n))) )
#endif
typedef struct {
u32 h0,h1,h2,h3,h4;
u32 nblocks;
unsigned char buf[64];
int count;
} SHA1_CONTEXT;
void
sha1_init( SHA1_CONTEXT *hd )
{
hd->h0 = 0x67452301;
hd->h1 = 0xefcdab89;
hd->h2 = 0x98badcfe;
hd->h3 = 0x10325476;
hd->h4 = 0xc3d2e1f0;
hd->nblocks = 0;
hd->count = 0;
}
/****************
* Transform the message X which consists of 16 32-bit-words
*/
static void
transform( SHA1_CONTEXT *hd, unsigned char *data )
{
u32 a,b,c,d,e,tm;
u32 x[16];
/* get values from the chaining vars */
a = hd->h0;
b = hd->h1;
c = hd->h2;
d = hd->h3;
e = hd->h4;
#ifdef BIG_ENDIAN_HOST
memcpy( x, data, 64 );
#else
{
int i;
unsigned char *p2;
for(i=0, p2=(unsigned char*)x; i < 16; i++, p2 += 4 )
{
p2[3] = *data++;
p2[2] = *data++;
p2[1] = *data++;
p2[0] = *data++;
}
}
#endif
#define K1 0x5A827999L
#define K2 0x6ED9EBA1L
#define K3 0x8F1BBCDCL
#define K4 0xCA62C1D6L
#define F1(x,y,z) ( z ^ ( x & ( y ^ z ) ) )
#define F2(x,y,z) ( x ^ y ^ z )
#define F3(x,y,z) ( ( x & y ) | ( z & ( x | y ) ) )
#define F4(x,y,z) ( x ^ y ^ z )
#define M(i) ( tm = x[i&0x0f] ^ x[(i-14)&0x0f] \
^ x[(i-8)&0x0f] ^ x[(i-3)&0x0f] \
, (x[i&0x0f] = rol(tm,1)) )
#define R(a,b,c,d,e,f,k,m) do { e += rol( a, 5 ) \
+ f( b, c, d ) \
+ k \
+ m; \
b = rol( b, 30 ); \
} while(0)
R( a, b, c, d, e, F1, K1, x[ 0] );
R( e, a, b, c, d, F1, K1, x[ 1] );
R( d, e, a, b, c, F1, K1, x[ 2] );
R( c, d, e, a, b, F1, K1, x[ 3] );
R( b, c, d, e, a, F1, K1, x[ 4] );
R( a, b, c, d, e, F1, K1, x[ 5] );
R( e, a, b, c, d, F1, K1, x[ 6] );
R( d, e, a, b, c, F1, K1, x[ 7] );
R( c, d, e, a, b, F1, K1, x[ 8] );
R( b, c, d, e, a, F1, K1, x[ 9] );
R( a, b, c, d, e, F1, K1, x[10] );
R( e, a, b, c, d, F1, K1, x[11] );
R( d, e, a, b, c, F1, K1, x[12] );
R( c, d, e, a, b, F1, K1, x[13] );
R( b, c, d, e, a, F1, K1, x[14] );
R( a, b, c, d, e, F1, K1, x[15] );
R( e, a, b, c, d, F1, K1, M(16) );
R( d, e, a, b, c, F1, K1, M(17) );
R( c, d, e, a, b, F1, K1, M(18) );
R( b, c, d, e, a, F1, K1, M(19) );
R( a, b, c, d, e, F2, K2, M(20) );
R( e, a, b, c, d, F2, K2, M(21) );
R( d, e, a, b, c, F2, K2, M(22) );
R( c, d, e, a, b, F2, K2, M(23) );
R( b, c, d, e, a, F2, K2, M(24) );
R( a, b, c, d, e, F2, K2, M(25) );
R( e, a, b, c, d, F2, K2, M(26) );
R( d, e, a, b, c, F2, K2, M(27) );
R( c, d, e, a, b, F2, K2, M(28) );
R( b, c, d, e, a, F2, K2, M(29) );
R( a, b, c, d, e, F2, K2, M(30) );
R( e, a, b, c, d, F2, K2, M(31) );
R( d, e, a, b, c, F2, K2, M(32) );
R( c, d, e, a, b, F2, K2, M(33) );
R( b, c, d, e, a, F2, K2, M(34) );
R( a, b, c, d, e, F2, K2, M(35) );
R( e, a, b, c, d, F2, K2, M(36) );
R( d, e, a, b, c, F2, K2, M(37) );
R( c, d, e, a, b, F2, K2, M(38) );
R( b, c, d, e, a, F2, K2, M(39) );
R( a, b, c, d, e, F3, K3, M(40) );
R( e, a, b, c, d, F3, K3, M(41) );
R( d, e, a, b, c, F3, K3, M(42) );
R( c, d, e, a, b, F3, K3, M(43) );
R( b, c, d, e, a, F3, K3, M(44) );
R( a, b, c, d, e, F3, K3, M(45) );
R( e, a, b, c, d, F3, K3, M(46) );
R( d, e, a, b, c, F3, K3, M(47) );
R( c, d, e, a, b, F3, K3, M(48) );
R( b, c, d, e, a, F3, K3, M(49) );
R( a, b, c, d, e, F3, K3, M(50) );
R( e, a, b, c, d, F3, K3, M(51) );
R( d, e, a, b, c, F3, K3, M(52) );
R( c, d, e, a, b, F3, K3, M(53) );
R( b, c, d, e, a, F3, K3, M(54) );
R( a, b, c, d, e, F3, K3, M(55) );
R( e, a, b, c, d, F3, K3, M(56) );
R( d, e, a, b, c, F3, K3, M(57) );
R( c, d, e, a, b, F3, K3, M(58) );
R( b, c, d, e, a, F3, K3, M(59) );
R( a, b, c, d, e, F4, K4, M(60) );
R( e, a, b, c, d, F4, K4, M(61) );
R( d, e, a, b, c, F4, K4, M(62) );
R( c, d, e, a, b, F4, K4, M(63) );
R( b, c, d, e, a, F4, K4, M(64) );
R( a, b, c, d, e, F4, K4, M(65) );
R( e, a, b, c, d, F4, K4, M(66) );
R( d, e, a, b, c, F4, K4, M(67) );
R( c, d, e, a, b, F4, K4, M(68) );
R( b, c, d, e, a, F4, K4, M(69) );
R( a, b, c, d, e, F4, K4, M(70) );
R( e, a, b, c, d, F4, K4, M(71) );
R( d, e, a, b, c, F4, K4, M(72) );
R( c, d, e, a, b, F4, K4, M(73) );
R( b, c, d, e, a, F4, K4, M(74) );
R( a, b, c, d, e, F4, K4, M(75) );
R( e, a, b, c, d, F4, K4, M(76) );
R( d, e, a, b, c, F4, K4, M(77) );
R( c, d, e, a, b, F4, K4, M(78) );
R( b, c, d, e, a, F4, K4, M(79) );
/* Update chaining vars */
hd->h0 += a;
hd->h1 += b;
hd->h2 += c;
hd->h3 += d;
hd->h4 += e;
}
/* Update the message digest with the contents
* of INBUF with length INLEN.
*/
static void
sha1_write( SHA1_CONTEXT *hd, unsigned char *inbuf, size_t inlen)
{
if( hd->count == 64 ) { /* flush the buffer */
transform( hd, hd->buf );
hd->count = 0;
hd->nblocks++;
}
if( !inbuf )
return;
if( hd->count ) {
for( ; inlen && hd->count < 64; inlen-- )
hd->buf[hd->count++] = *inbuf++;
sha1_write( hd, NULL, 0 );
if( !inlen )
return;
}
while( inlen >= 64 ) {
transform( hd, inbuf );
hd->count = 0;
hd->nblocks++;
inlen -= 64;
inbuf += 64;
}
for( ; inlen && hd->count < 64; inlen-- )
hd->buf[hd->count++] = *inbuf++;
}
/* The routine final terminates the computation and
* returns the digest.
* The handle is prepared for a new cycle, but adding bytes to the
* handle will the destroy the returned buffer.
* Returns: 20 bytes representing the digest.
*/
static void
sha1_final(SHA1_CONTEXT *hd)
{
u32 t, msb, lsb;
unsigned char *p;
sha1_write(hd, NULL, 0); /* flush */;
t = hd->nblocks;
/* multiply by 64 to make a byte count */
lsb = t << 6;
msb = t >> 26;
/* add the count */
t = lsb;
if( (lsb += hd->count) < t )
msb++;
/* multiply by 8 to make a bit count */
t = lsb;
lsb <<= 3;
msb <<= 3;
msb |= t >> 29;
if( hd->count < 56 ) { /* enough room */
hd->buf[hd->count++] = 0x80; /* pad */
while( hd->count < 56 )
hd->buf[hd->count++] = 0; /* pad */
}
else { /* need one extra block */
hd->buf[hd->count++] = 0x80; /* pad character */
while( hd->count < 64 )
hd->buf[hd->count++] = 0;
sha1_write(hd, NULL, 0); /* flush */;
memset(hd->buf, 0, 56 ); /* fill next block with zeroes */
}
/* append the 64 bit count */
hd->buf[56] = msb >> 24;
hd->buf[57] = msb >> 16;
hd->buf[58] = msb >> 8;
hd->buf[59] = msb ;
hd->buf[60] = lsb >> 24;
hd->buf[61] = lsb >> 16;
hd->buf[62] = lsb >> 8;
hd->buf[63] = lsb ;
transform( hd, hd->buf );
p = hd->buf;
#ifdef BIG_ENDIAN_HOST
#define X(a) do { *(u32*)p = hd->h##a ; p += 4; } while(0)
#else /* little endian */
#define X(a) do { *p++ = hd->h##a >> 24; *p++ = hd->h##a >> 16; \
*p++ = hd->h##a >> 8; *p++ = hd->h##a; } while(0)
#endif
X(0);
X(1);
X(2);
X(3);
X(4);
#undef X
}
更多詳情見請繼續閱讀下一頁的精彩內容： http://www.linuxidc.com/Linux/2014-06/103727p2.htm