【逆向基础】密码学实现（SHA1）

引例：海博TV

思路：抓包发现请求头有一些Signature加密，简单的用一个java层自吐。发现没有hook到。这时候盲猜在so。试试search 【System.loadLibrary("】与本包名有关的刚好就一个找到hook一下接下来就是 bbbbbblalala 的跟着流程往下找在so中找到sha1。

emmm，这里的话是在libm2o_jni.so, 传入的明文是个地址( &p )，因此hook时需要

hexdump(ptr.readPointert())

snprintf ( )

SHA1：

基本思路都是将信息分成N个分组，每组64个字节（512 位），每个分组都进行摘要运算。

当一个分组的摘要运算完毕后，将上一个分组的结果也用于下一个分组的运算。

当最后一个分组长度小于448 b那么会加上0x80 然后补足448 ，在最后64位为长度标识，大端序

=========================================================================

对压入数据的处理：（以 ”abc“ 为例）

61 62 63 80 00 00 00 00 00 00 00 00 00 00 00 00 61 62 63 对应 97 98 99 即 a b c

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x80 对应128 二进制10000000

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 18 18代表24位即明文所占bit

因共有64位表示数据大小

那么sha1 的摘要极限是2的63次方

=========================================================================

SO：sha1_encode：

1.SHA1_Init(v10);

int __fastcall SHA1_Init(_DWORD *a1)
{int result; // r0memset(a1, 0, 0x60u);a1[1] = -271733879; //0xEFCDAB89;*a1 = 1732584193;   //0x67452301;result = 1;a1[2] = -1732584194;//0x98BADCFE;a1[3] = 271733878;  //0x10325476;a1[4] = -1009589776;//0xC3D2E1F0;return result;
}

初始化常量

0x67452301;
0xEFCDAB89;
0x98BADCFE;
0x10325476;
0xC3D2E1F0;

2.SHA1_Update((int)v10, a1);

//压入数据
int SHA1Input(SHA1Context *context, const uint8_t *message_array, unsigned length) {while (length-- && !context->Corrupted) {context->Message_Block[context->Message_Block_Index++] = (*message_array & 0xFF);context->Length_Low += 8;if (context->Length_Low == 0) {context->Length_High++;if (context->Length_High == 0) {/* Message is too long */context->Corrupted = 1;}}//如果当前index = 64 那么先进行一轮计算if (context->Message_Block_Index == 64) { SHA1ProcessMessageBlock(context);}message_array++;}return shaSuccess;
}

3.SHA1_Final();

void SHA1ProcessMessageBlock(SHA1Context *context) {const uint32_t K[] = { /*  SHA1 的K表 */0x5A827999,0x6ED9EBA1,0x8F1BBCDC,0xCA62C1D6};int t; /* Loop counter */uint32_t temp; /* Temporary word value */uint32_t W[80]; /* Word sequence */uint32_t A, B, C, D, E; /* Word buffers *//** Initialize the first 16 words in the array W*/for (t = 0; t < 16; t++) {W[t] = context->Message_Block[t * 4] << 24;W[t] |= context->Message_Block[t * 4 + 1] << 16;W[t] |= context->Message_Block[t * 4 + 2] << 8;W[t] |= context->Message_Block[t * 4 + 3];}for (t = 16; t < 80; t++) {W[t] = SHA1CircularShift(1, W[t - 3] ^ W[t - 8] ^ W[t - 14] ^ W[t - 16]);//W[t] = W[t - 3] ^ W[t - 8] ^ W[t - 14] ^ W[t - 16];}A = context->Intermediate_Hash[0];B = context->Intermediate_Hash[1];C = context->Intermediate_Hash[2];D = context->Intermediate_Hash[3];E = context->Intermediate_Hash[4];for (t = 0; t < 20; t++) {temp = SHA1CircularShift(5, A) +((B & C) | ((~B) & D)) + E + W[t] + K[0];E = D;D = C;C = SHA1CircularShift(30, B);B = A;A = temp;}for (t = 20; t < 40; t++) {temp = SHA1CircularShift(5, A) + (B ^ C ^ D) + E + W[t] + K[1];E = D;D = C;C = SHA1CircularShift(30, B);B = A;A = temp;}for (t = 40; t < 60; t++) {temp = SHA1CircularShift(5, A) +((B & C) | (B & D) | (C & D)) + E + W[t] + K[2];E = D;D = C;C = SHA1CircularShift(30, B);B = A;A = temp;}for (t = 60; t < 80; t++) {temp = SHA1CircularShift(5, A) + (B ^ C ^ D) + E + W[t] + K[3];E = D;D = C;C = SHA1CircularShift(30, B);B = A;A = temp;}context->Intermediate_Hash[0] += A;context->Intermediate_Hash[1] += B;context->Intermediate_Hash[2] += C;context->Intermediate_Hash[3] += D;context->Intermediate_Hash[4] += E;context->Message_Block_Index = 0;
}

#SHA1 pad

void SHA1PadMessage(SHA1Context *context) {/** Check to see if the current message block is too small to hold* the initial padding bits and length. If so, we will pad the* block, process it, and then continue padding into a second* block.*/if (context->Message_Block_Index > 55) {context->Message_Block[context->Message_Block_Index++] = 0x80;while (context->Message_Block_Index < 64) {context->Message_Block[context->Message_Block_Index++] = 0;}SHA1ProcessMessageBlock(context);while (context->Message_Block_Index < 56) {context->Message_Block[context->Message_Block_Index++] = 0;}} else {context->Message_Block[context->Message_Block_Index++] = 0x80;while (context->Message_Block_Index < 56) {context->Message_Block[context->Message_Block_Index++] = 0;}}/** Store the message length as the last 8 octets*/context->Message_Block[56] = context->Length_High >> 24;context->Message_Block[57] = context->Length_High >> 16;context->Message_Block[58] = context->Length_High >> 8;context->Message_Block[59] = context->Length_High;context->Message_Block[60] = context->Length_Low >> 24;context->Message_Block[61] = context->Length_Low >> 16;context->Message_Block[62] = context->Length_Low >> 8;context->Message_Block[63] = context->Length_Low;SHA1ProcessMessageBlock(context);
}