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The DES library.

Please note that this library was originally written to operate with

eBones, a version of Kerberos that had had encryption removed when it left

the USA and then put back in. As such there are some routines that I will

advise not using but they are still in the library for historical reasons.

For all calls that have an 'input' and 'output' variables, they can be the

same.

This library requires the inclusion of 'des.h'.

All of the encryption functions take what is called a des_key_schedule as

be a multiple of 8 bytes.

The define DES_ENCRYPT is passed to specify encryption, DES_DECRYPT to

specify decryption. The functions and global variable are as follows:

int des_check_key;

DES keys are supposed to be odd parity. If this variable is set to

a non-zero value, des_set_key() will check that the key has odd

parity and is not one of the known weak DES keys. By default this

variable is turned off;

void des_set_odd_parity(

des_cblock *key );

key are 1/2^52 so it is probably not worth checking for them.

int des_set_key(

des_cblock *key,

des_key_schedule schedule);

Des_set_key converts an 8 byte DES key into a des_key_schedule.

A des_key_schedule is an expanded form of the key which is used to

perform actual encryption. It can be regenerated from the DES key

so it only needs to be kept when encryption or decryption is about

to occur. Don't save or pass around des_key_schedule's since they

are CPU architecture dependent, DES keys are not. If des_check_key

des_key_schedule schedule);

int des_rw_mode; /* defaults to DES_PCBC_MODE */

This flag holds either DES_CBC_MODE or DES_PCBC_MODE (default).

This specifies the function to use in the enc_read() and enc_write()

functions.

unsigned long *data,

des_key_schedule ks,

int enc);

This is the DES encryption function that gets called by just about

have a look at my source code for more details on how I use this

function.

Data is a pointer to 2 unsigned long's and ks is the

des_key_schedule to use. enc, is non zero specifies encryption,

zero if decryption.

void des_encrypt2(

unsigned long *data,

des_key_schedule ks,

int enc);

This functions is the same as des_encrypt() except that the DES

initial permutation (IP) and final permutation (FP) have been left

out. As for des_encrypt(), you should not use this function.

IP() des_encrypt2() des_encrypt2() des_encrypt2() FP() is the same

des_key_schedule ks,

int enc);

This is the basic Electronic Code Book form of DES, the most basic

form. Input is encrypted into output using the key represented by

ks. If enc is non zero (DES_ENCRYPT), encryption occurs, otherwise

decryption occurs. Input is 8 bytes long and output is 8 bytes.

(the des_cblock structure is 8 chars).

void des_ecb3_encrypt(

des_cblock *input,

des_cblock *output,

des_key_schedule ks3,

the 8 bytes of input is encrypted with ks1, decrypted with ks2 and

C=E(ks3,D(ks2,E(ks1,M))). There is a macro, des_ecb2_encrypt()

that only takes 2 des_key_schedules that implements,

C=E(ks1,D(ks2,E(ks1,M))) in that the final encrypt is done with ks1.

void des_cbc_encrypt(

des_cblock *input,

long length,

des_key_schedule ks,

des_cblock *ivec,

int enc);

not being held responsible :-). ivec is the initialisation vector.

This function does not modify this variable. To correctly implement

cbc mode, you need to do one of 2 things; copy the last 8 bytes of

cipher text for use as the next ivec in your application,

or use des_ncbc_encrypt().

Only this routine has this problem with updating the ivec, all

other routines that are implementing cbc mode update ivec.

void des_ncbc_encrypt(

des_cblock *input,

des_cblock *output,

long length,

des_key_schedule sk,

int enc);

des_cbc_encrypt accept that ivec is updates with the correct value

to pass in subsequent calls to des_ncbc_encrypt(). I advise using

des_ncbc_encrypt() instead of des_cbc_encrypt();

void des_3cbc_encrypt(

des_cblock *input,

des_cblock *output,

long length,

des_key_schedule sk1,

des_key_schedule sk2,

des_cblock *ivec1,

This function is flawed, do not use it. I have left it in the