如何使用SHA1散列C编程 [英] How to use SHA1 hashing in C programming

问题描述

我试图写证明SHA1是免费的近碰撞C程序，但我想不出如何实际创建我的输入值的哈希值。我只需要创建哈希和十六进制值存储到一个数组。一些谷歌搜索后，我发现OpenSSL文档指导我使用这个：

I am trying to write a C program that proves SHA1 is nearly collision free, but I cannot figure out how to actually create the hash for my input values. I just need to create the hash, and store the hex value into an array. After some Google searches, I've found OpenSSL documentation directing me to use this:

 #include <openssl/sha.h>

 unsigned char *SHA1(const unsigned char *d, unsigned long n,
                  unsigned char *md);

 int SHA1_Init(SHA_CTX *c);
 int SHA1_Update(SHA_CTX *c, const void *data,
                  unsigned long len);
 int SHA1_Final(unsigned char *md, SHA_CTX *c);

我相信我应该是使用操作无符号的char * SHA1或SHA1_Init，但我不知道的论点是什么，给定x是我的输入进行哈希运算。会有人请清除此为我？谢谢你。

I believe I should be using either unsigned char *SHA1 or SHA1_Init, but I am not sure what the arguments would be, given x is my input to be hashed. Would someone please clear this up for me? Thanks.

推荐答案

如果你把所有的数据一次，只需要使用 SHA1 功能：

If you have all of your data at once, just use the SHA1 function:

// The data to be hashed
char data[] = "Hello, world!";
size_t length = sizeof(data);

unsigned char hash[SHA_DIGEST_LENGTH];
SHA1(data, length, hash);
// hash now contains the 20-byte SHA-1 hash

如果，在另一方面，你只能得到你的数据在同一时间一块，你要计算哈希值，你收到的数据，然后使用其他功能：

If, on the other hand, you only get your data one piece at a time and you want to compute the hash as you receive that data, then use the other functions:

// Error checking omitted for expository purposes

// Object to hold the current state of the hash
SHA_CTX ctx;
SHA1_Init(&ctx);

// Hash each piece of data as it comes in:
SHA1_Update(&ctx, "Hello, ", 7);
...
SHA1_Update(&ctx, "world!", 6);
// etc.
...
// When you're done with the data, finalize it:
unsigned char hash[SHA_DIGEST_LENGTH];
SHA1_Final(hash, &ctx);

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