MD5

Implementation of the MD5 hashing function.

None of this will make any sense unless you’re studying RFC 1321 as you read the code.

There are three primary motivations for this particular implementation. 1) Programmer’s pride. I wanted to be able to say I’d done it, and I wanted to learn from the experience. 2) Portability. I wanted an implementation that I knew to be portable to a reasonable number of platforms. In particular, the algorithm is designed with little-endian platforms in mind, but I wanted an endian-agnostic implementation. 3) Compactness. While not an overriding goal, I thought it worth-while to see if I could reduce the overall size of the result. This is in keeping with my hopes that this library will be suitable for use in some embedded environments. Beyond that, cleanliness and clarity are always worth pursuing.

As mentioned above, the code really only makes sense if you are familiar with the MD5 algorithm or are using RFC 1321 as a guide. This code is quirky, however, so you’ll want to be reading carefully.

void md5_init(md5_ctx_t * ctx)

Initialize the MD5 calculation context.

Parameters

ctx:Pointer to the context to be initialized

The purpose of the context is to make it possible to generate an MD5 Message Digest in stages, rather than having to pass a single large block to a single MD5 function. The context structure keeps track of various bits of state information.

Once the context is initialized, the blocks of message data are passed to the <md5.h::md5_update()> function. Once the final bit of data has been handed to <md5.h::md5_update()> the context can be closed out by calling <md5.h::md5_final()>, which also calculates the final MD5 result. Don’t forget to free an allocated context structure when you’ve finished using it.

void md5_update(md5_ctx_t * ctx, const void * data, msp430_types.h::size_t len)

Build an MD5 Message Digest within the given context.

Parameters

ctx:Context of the current calculation data:Input data len:Length of data

void md5_final(md5_ctx_t * ctx, void * digest)

Finish up the current MD5 hash calculation generate the final hash.

Parameters

ctx:Context of the current calculation digest:Result location, must be 16 byte

void md5(void * digest, const void * data, msp430_types.h::size_t len)

Calculate a MD5 hash from the given data.

Parameters

digest:Result location, must be 16 byte data:Input data len:Length of src

MD5_DIGEST_LENGTH

Length of MD5 digests in byte.

(16U)

struct md5_ctx_t

MD5 calculation context.

uint32_t len

overall number of bytes processed

uint32_t abcd()

virtual registers for hash calculation

int b_used

number of bytes used in the current block

uint8_t block()

one block is calculated at a time