How to create a md5 hash of a string in C?

Question

I've found some md5 code that consists of the following prototypes...

I've been trying to find out where I have to put the string I want to hash, what functions I need to call, and where to find the string once it has been hashed. I'm confused with regards to what the uint32 buf[4] and uint32 bits[2] are in the struct.

struct MD5Context {     uint32 buf[4];     uint32 bits[2];     unsigned char in[64]; };  /*  * Start MD5 accumulation.  Set bit count to 0 and buffer to mysterious  * initialization constants.  */ void MD5Init(struct MD5Context *context);  /*  * Update context to reflect the concatenation of another buffer full  * of bytes.  */ void MD5Update(struct MD5Context *context, unsigned char const *buf, unsigned len);  /*  * Final wrapup - pad to 64-byte boundary with the bit pattern   * 1 0* (64-bit count of bits processed, MSB-first)  */ void MD5Final(unsigned char digest[16], struct MD5Context *context);  /*  * The core of the MD5 algorithm, this alters an existing MD5 hash to  * reflect the addition of 16 longwords of new data.  MD5Update blocks  * the data and converts bytes into longwords for this routine.  */ void MD5Transform(uint32 buf[4], uint32 const in[16]); 

Answer 1

I don't know this particular library, but I've used very similar calls. So this is my best guess:

unsigned char digest[16]; const char* string = "Hello World"; struct MD5Context context; MD5Init(&context); MD5Update(&context, string, strlen(string)); MD5Final(digest, &context); 

This will give you back an integer representation of the hash. You can then turn this into a hex representation if you want to pass it around as a string.

char md5string[33]; for(int i = 0; i < 16; ++i)     sprintf(&md5string[i*2], "%02x", (unsigned int)digest[i]);