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103 lines
2.2 KiB
103 lines
2.2 KiB
3 months ago
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Hashing routines
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================
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LibUCW contains implementations of several hash algorithms.
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<<crypto,Cryptographic hashes>>:
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- <<md5,MD5>> (RFC 1321)
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- <<sha1,SHA1>> (RFC 3174)
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- <<hash:sha1_hmac(),SHA1_HMAC message authentication>> (RFC 2104)
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- <<usage,Common usage>>
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<<checksum,Checksums>>:
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- <<crypto:adler,Adler-32>>
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- <<crc,CRC>>
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<<nocrypto,Non-cryptographic hashes>>:
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- <<strhash,String & block hashes>>
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- <<inthash,Integer hashes>>
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[[crypto]]
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Cryptographic hashes
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--------------------
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[[md5]]
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MD5
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~~~
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!!ucw/md5.h
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[[sha1]]
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SHA1
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~~~~
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!!ucw/sha1.h
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[[usage]]
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Common usage
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~~~~~~~~~~~~
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There are two ways you can use the hashing routines.
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- Single-shot interface. If you have an in-memory buffer of the whole
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message you want to hash, you can use this.
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char *message = "Hello world";
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byte output[MD5_SIZE];
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md5_hash_buffer(output, message, strlen(message));
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- Multi-shot interface. If you have the message scattered in many
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buffers or you get it by parts, you do not need to concatenate the
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parts together.
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byte buffer[MAX_BUFFER];
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uint buffer_len;
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md5_context c;
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md5_init(&c);
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while(buffer_len = get_chunk(buffer, MAX_BUFFER)) {
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md5_update(&c, buffer, buffer_len);
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}
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byte output[MD5_SIZE];
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memcpy(output, md5_final(&c), MD5_SIZE);
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SHA1 has the same interface, so the same two ways apply.
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See also <<string:mem_to_hex()>>.
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[[checksum]]
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Checksums
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---------
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Their purpose is checking against random data changes, hardware
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failures and alike. They are not to be used against aimed attacks.
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Adler-32
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~~~~~~~~
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The <<compress:adler,Adler-32 checksum>> is documented in the
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<<compress:,compression capter>>.
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CRC-32
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~~~~~~
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32-bit Cyclic Redundancy Check with the polynomial suggested by
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Castagnoli et al.: Optimization of Cyclic Redundancy-Check Codes
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with 24 and 32 Parity Bits", IEEE Trans. on Communications, Vol. 41,
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No. 6, 1993.
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The interface is similar to the one we use for the cryptographic hashes.
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!!ucw/crc.h
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[[nocrypto]]
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Non-cryptographic hashes
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------------------------
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They are usually used to identify values in hash tables.
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All these functions expect to be moduled by the size of a hash table.
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The size should be a prime number (it gives better distribution).
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!!ucw/hashfunc.h
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