.TH DES 3 "04 October 1993" "Linux" "Linux Programmer's Manual".SH NAMEdesinit, setkey, endes, dedes, desdone - DES encryption.SH SYNOPSIS.PP.B desinit(mode).B int mode;.PP.B setkey(key).B char *key;.PP.B endes(block).B char *block;.PP.B dedes(block).B char *block;.PP.B desdone();.SH DESCRIPTIONThese routines implement both standard and modified forms of the NBS DataEncryption Standard (DES). The user must first call.B desinitwith one of three operating modes:.PP0 - Standard, vanilla DES..PP1 - DES with the initial and final permutations removed.As these permutations do not strengthen the algorithm,they are widely regarded as having no purpose other than to slowdown software implementations.Removing them speeds it up but of course the algorithm is no longer standardand it will not be compatible with hardware DES chips..PP2 - DES with the initial and final permutations removed, and with independent48-bit subkeys for each of the 16 rounds. Needless to say this is evenless standard than mode 1, but if properly used (randomize ALL key bytes --no padding!) it should strengthen the algorithm..PPAfter calling.B desinitthe user next calls.B setkey.In modes 0 and 1, 8 key bytes are expected, with the low order bit ofeach key byte ignored (parity is not checked). This gives a 56-bit key.In mode 2, 128 key bytes are expected; the high order 2 bits of each byte areignored, giving a 768 bit key.In this mode, the first 8 bytes will be used in the first round, thesecond 8 bytes in the second round, and so on..PPOnce the key is set, the user may perform in-place encryption and decryptionof 8-byte blocks of data with calls to.B endesand.B dedes..PPTo free up memory dynamically allocated by.B desinitthe user may call.B desdone.If further encryption or decryption is to be done,.B desinitand.B setkeymust be called again..SH AUTHORSPhil Karn, KA9Q, building heavily on the earlier public domain codeby Jim Gillogly.Chris Cappuccio (chris@g386bsd.first.gmd.de)