Hash Library

The hash library can be used to compute hash values and HMACs. The following algorithms are supported:

MD4
MD5
SHA1
SHA224
SHA256
SHA384
SHA512

File information

File	common/ilib/hash.h
Classes	hash hmac
Data types	hash_t
Examples	Calculating a SHA256 hash Calculating HMAC-SHA1

Classes

hash

class hash {
    ulong64 context[27];
    hash_t type;
public:
    hash();
    void init(hash_t type);
    void update(const void * in, size_t len);
    void final(void * out);
    void copy(class hash * from);
    size_t size();
};

Overview

The hash class defines a uniform interface for calculating hashes using different algorithms.

Hash functions process an arbitrary number of bytes, possibly devided into chunks, and produce a fixed number of output bytes. The output is called a "hash" or "digest". The same input data always produces the same digest. So hashes can be used for integrity protection of messages. Cryptographically strong hash functions like SHA256 make it very hard (aka impossible) to gain any information about the input from the produced digest. So they are often used for digital signatures and login protocols.

Public functions

init

Initializes the internal state of the object and sets the algorithm to be used.

Parameters

hash_t type

The hash algorithm to be used.

Remarks

The init function has to be called before using any other functions of the object.

update

Processes a chunk of input data.

Parameters

const void * in	The input buffer.
size_t len	The number of bytes to be processed.

Remarks

This function can be called mupltiple times.

final

Calculates the hash and copies the value to the given out buffer.

Parameters

void * out

The output buffer to write the hash value in binary form. The buffer size must match the hash size defined by the algorithm.

Remarks

The size function can be used to determine the needed output buffer size.

copy

Copies the internal state from the given other hash.

Parameters

class hash * from

A pointer to another hash object that shall be duplicated.

size

Return value

size_t

The size of the hash value for the current algorithm. This is the number of bytes that is written by function final to the out buffer.

Data types

Defines / Statics

HASH_SIZE_MD4	MD4 hashes use 16 bytes
HASH_SIZE_MD5	MD5 hashes use 16 bytes
HASH_SIZE_SHA1	SHA1 hashes use 20 bytes
HASH_SIZE_SHA224	SHA224 hashes use 28 bytes
HASH_SIZE_SHA256	SHA256 hashes use 32 bytes
HASH_SIZE_SHA384	SHA384 hashes use 48 bytes
HASH_SIZE_SHA512	SHA512 hashes use 64 bytes
HASH_SIZE_MAX	The maximum hash size produced by the library.

hash_t

enum hash_t {
    HASH_UNDEFINED,
    HASH_MD4,
    HASH_MD5,
    HASH_SHA1,
    HASH_SHA224,
    HASH_SHA256,
    HASH_SHA384,
    HASH_SHA512
};

Overview

The hash_t enum defines all hash algorithms supported by the library.

Values

HASH_UNDEFINED	Used internally to identify uninitialized objects.
HASH_MD4	Considered as cryptographically weak.
HASH_MD5	Considered as cryptographically weak.
HASH_SHA1	Considered as cryptographically weak.
HASH_SHA224
HASH_SHA256
HASH_SHA384
HASH_SHA512

Remarks

The old algorithms MD4, MD5 and SHA1 are insecure. They should not be used for new projects. Please use the algorithms of the SHA2 family (SHA224, SHA256, SHA384 or SHA512).

Code Example

Calculating a SHA256 hash

hash h;
byte out[32];
h.init(HASH_SHA256);
h.update(data1, 16);
h.update(data2, 5);
h.final(out);

Calculating HMAC-SHA1

hmac h;
byte out[HASH_SIZE_SHA1];
h.init(HASH_SHA1, key, key_len);
h.update(data1, 16);
h.update(data2, 5);
h.final(out);