des_crypt(3)
- NetBSD Manual Pages
DES_CRYPT(3) DES_CRYPT(3)
NAME
des_read_password, des_string_to_key, des_random_key,
des_set_key, des_ecb_encrypt, des_cbc_encrypt,
des_pcbc_encrypt, des_cbc_cksum, des_quad_cksum, - (new)
DES encryption
SYNOPSIS
#include <des.h>
int des_read_password(key,prompt,verify)
des_cblock *key;
char *prompt;
int verify;
int des_string_to_key(str,key)
char *str;
des_cblock key;
int des_random_key(key)
des_cblock *key;
int des_set_key(key,schedule)
des_cblock *key;
des_key_schedule schedule;
int des_ecb_encrypt(input,output,schedule,encrypt)
des_cblock *input;
des_cblock *output;
des_key_schedule schedule;
int encrypt;
int des_cbc_encrypt(input,output,length,schedule,ivec,encrypt)
des_cblock *input;
des_cblock *output;
long length;
des_key_schedule schedule;
des_cblock *ivec;
int encrypt;
int des_pcbc_encrypt(input,output,length,schedule,ivec,encrypt)
des_cblock *input;
des_cblock *output;
long length;
des_key_schedule schedule;
des_cblock *ivec;
int encrypt;
unsigned long des_cbc_cksum(input,output,length,schedule,ivec)
des_cblock *input;
des_cblock *output;
long length;
des_key_schedule schedule;
des_cblock *ivec;
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unsigned long quad_cksum(input,output,length,out_count,seed)
des_cblock *input;
des_cblock *output;
long length;
int out_count;
des_cblock *seed;
DESCRIPTION
This library supports various DES encryption related oper-
ations. It differs from the crypt, setkey, and encrypt
library routines in that it provides a true DES encryp-
tion, without modifying the algorithm, and executes much
faster.
For each key that may be simultaneously active, create a
des_key_schedule struct, defined in "des.h". Next, create
key schedules (from the 8-byte keys) as needed, via
des_set_key, prior to using the encryption or checksum
routines. Then setup the input and output areas. Make
sure to note the restrictions on lengths being multiples
of eight bytes. Finally, invoke the encryption/decryption
routines, des_ecb_encrypt or des_cbc_encrypt or
des_pcbc_encrypt, or, to generate a cryptographic check-
sum, use quad_cksum (fast) or des_cbc_cksum (slow).
A des_cblock struct is an 8 byte block used as the funda-
mental unit for DES data and keys, and is defined as:
typedef unsigned char des_cblock[8];
and a des_key_schedule, is defined as:
typedef struct des_ks_struct {des_cblock _;}
des_key_schedule[16];
des_read_password writes the string specified by prompt to
the standard output, turns off echo (if possible) and
reads an input string from standard input until terminated
with a newline. If verify is non-zero, it prompts and
reads input again, for use in applications such as chang-
ing a password; both versions are compared, and the input
is requested repeatedly until they match. Then
des_read_password converts the input string into a valid
DES key, internally using the des_string_to_key routine.
The newly created key is copied to the area pointed to by
the key argument. des_read_password returns a zero if no
errors occurred, or a -1 indicating that an error occurred
trying to manipulate the terminal echo.
des_string_to_key converts an arbitrary length null-termi-
nated string to an 8 byte DES key, with odd byte parity,
per FIPS specification. A one-way function is used to
MIT Project Athena Kerberos Version 4.0 2
DES_CRYPT(3) DES_CRYPT(3)
convert the string to a key, making it very difficult to
reconstruct the string from the key. The str argument is
a pointer to the string, and key should point to a
des_cblock supplied by the caller to receive the generated
key. No meaningful value is returned. Void is not used
for compatibility with other compilers.
des_random_key generates a random DES encryption key
(eight bytes), set to odd parity per FIPS specifications.
This routine uses the current time, process id, and a
counter as a seed for the random number generator. The
caller must supply space for the output key, pointed to
by argument key, then after calling des_random_key should
call the des_set_key routine when needed. No meaningful
value is returned. Void is not used for compatibility
with other compilers.
des_set_key calculates a key schedule from all eight bytes
of the input key, pointed to by the key argument, and out-
puts the schedule into the des_key_schedule indicated by
the schedule argument. Make sure to pass a valid eight
byte key; no padding is done. The key schedule may then
be used in subsequent encryption/decryption/checksum oper-
ations. Many key schedules may be cached for later use.
The user is responsible to clear keys and schedules as
soon as no longer needed, to prevent their disclosure.
The routine also checks the key parity, and returns a zero
if the key parity is correct (odd), a -1 indicating a key
parity error, or a -2 indicating use of an illegal weak
key. If an error is returned, the key schedule was not
created.
des_ecb_encrypt is the basic DES encryption routine that
encrypts or decrypts a single 8-byte block in electronic
code book mode. It always transforms the input data,
pointed to by input, into the output data, pointed to by
the output argument.
If the encrypt argument is non-zero, the input (cleartext)
is encrypted into the output (ciphertext) using the
key_schedule specified by the schedule argument, previ-
ously set via des_set_key
If encrypt is zero, the input (now ciphertext) is
decrypted into the output (now cleartext).
Input and output may overlap.
No meaningful value is returned. Void is not used for
compatibility with other compilers.
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des_cbc_encrypt encrypts/decrypts using the cipher-block-
chaining mode of DES. If the encrypt argument is non-
zero, the routine cipher-block-chain encrypts the cleart-
ext data pointed to by the input argument into the cipher-
text pointed to by the output argument, using the key
schedule provided by the schedule argument, and initial-
ization vector provided by the ivec argument. If the
length argument is not an integral multiple of eight
bytes, the last block is copied to a temp and zero filled
(highest addresses). The output is ALWAYS an integral
multiple of eight bytes.
If encrypt is zero, the routine cipher-block chain
decrypts the (now) ciphertext data pointed to by the input
argument into (now) cleartext pointed to by the output
argument using the key schedule provided by the schedule
argument, and initialization vector provided by the ivec
argument. Decryption ALWAYS operates on integral multiples
of 8 bytes, so it will round the length provided up to the
appropriate multiple. Consequently, it will always produce
the rounded-up number of bytes of output cleartext. The
application must determine if the output cleartext was
zero-padded due to original cleartext lengths that were
not integral multiples of 8.
No errors or meaningful values are returned. Void is not
used for compatibility with other compilers.
A characteristic of cbc mode is that changing a single bit
of the cleartext, then encrypting using cbc mode, affects
ALL the subsequent ciphertext. This makes cryptanalysis
much more difficult. However, modifying a single bit of
the ciphertext, then decrypting, only affects the result-
ing cleartext from the modified block and the succeeding
block. Therefore, des_pcbc_encrypt is STRONGLY recom-
mended for applications where indefinite propagation of
errors is required in order to detect modifications.
des_pcbc_encrypt encrypts/decrypts using a modified block
chaining mode. Its calling sequence is identical to
des_cbc_encrypt. It differs in its error propagation
characteristics.
des_pcbc_encrypt is highly recommended for most encryption
purposes, in that modification of a single bit of the
ciphertext will affect ALL the subsequent (decrypted)
cleartext. Similarly, modifying a single bit of the clear-
text will affect ALL the subsequent (encrypted) cipher-
text. "PCBC" mode, on encryption, "xors" both the cleart-
ext of block N and the ciphertext resulting from block N
with the cleartext for block N+1 prior to encrypting block
N+1.
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DES_CRYPT(3) DES_CRYPT(3)
des_cbc_cksum produces an 8 byte cryptographic checksum by
cipher-block-chain encrypting the cleartext data pointed
to by the input argument. All of the ciphertext output is
discarded, except the last 8-byte ciphertext block, which
is written into the area pointed to by the output argu-
ment. It uses the key schedule, provided by the schedule
argument and initialization vector provided by the ivec
argument. If the length argument is not an integral mul-
tiple of eight bytes, the last cleartext block is copied
to a temp and zero filled (highest addresses). The output
is ALWAYS eight bytes.
The routine also returns an unsigned long, which is the
last (highest address) half of the 8 byte checksum com-
puted.
quad_cksum produces a checksum by chaining quadratic oper-
ations on the cleartext data pointed to by the input argu-
ment. The length argument specifies the length of the
input -- only exactly that many bytes are included for the
checksum, without any padding.
The algorithm may be iterated over the same input data, if
the out_count argument is 2, 3 or 4, and the optional out-
put argument is a non-null pointer . The default is one
iteration, and it will not run more than 4 times. Multiple
iterations run slower, but provide a longer checksum if
desired. The seed argument provides an 8-byte seed for the
first iteration. If multiple iterations are requested, the
results of one iteration are automatically used as the
seed for the next iteration.
It returns both an unsigned long checksum value, and if
the output argument is not a null pointer, up to 16 bytes
of the computed checksum are written into the output.
FILES
/usr/include/des.h
/usr/lib/libdes.a
SEE ALSO
DIAGNOSTICS
BUGS
This manual page may not correspond exactly to the version
of libdes which is included with the version of Kerberos
which you are using.
AUTHORS
Steve Miller, MIT Project Athena/Digital Equipment Corpo-
ration
MIT Project Athena Kerberos Version 4.0 5
DES_CRYPT(3) DES_CRYPT(3)
RESTRICTIONS
COPYRIGHT 1985,1986 Massachusetts Institute of Technology
This software may not be exported outside of the US with-
out a special license from the US Dept of Commerce. It may
be replaced by any secret key block cipher with block
length and key length of 8 bytes, as long as the interface
is the same as described here.
MIT Project Athena Kerberos Version 4.0 6
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