# des.3ssl man page

DES_random_key, DES_set_key, DES_key_sched, DES_set_key_checked, DES_set_key_unchecked, DES_set_odd_parity, DES_is_weak_key, DES_ecb_encrypt, DES_ecb2_encrypt, DES_ecb3_encrypt, DES_ncbc_encrypt, DES_cfb_encrypt, DES_ofb_encrypt, DES_pcbc_encrypt, DES_cfb64_encrypt, DES_ofb64_encrypt, DES_xcbc_encrypt, DES_ede2_cbc_encrypt, DES_ede2_cfb64_encrypt, DES_ede2_ofb64_encrypt, DES_ede3_cbc_encrypt, DES_ede3_cbcm_encrypt, DES_ede3_cfb64_encrypt, DES_ede3_ofb64_encrypt, DES_cbc_cksum, DES_quad_cksum, DES_string_to_key, DES_string_to_2keys, DES_fcrypt, DES_crypt, DES_enc_read, DES_enc_write — DES encryption

## Synopsis

```
#include <openssl/des.h>
void DES_random_key(DES_cblock *ret);
int DES_set_key(const_DES_cblock *key, DES_key_schedule *schedule);
int DES_key_sched(const_DES_cblock *key, DES_key_schedule *schedule);
int DES_set_key_checked(const_DES_cblock *key,
DES_key_schedule *schedule);
void DES_set_key_unchecked(const_DES_cblock *key,
DES_key_schedule *schedule);
void DES_set_odd_parity(DES_cblock *key);
int DES_is_weak_key(const_DES_cblock *key);
void DES_ecb_encrypt(const_DES_cblock *input, DES_cblock *output,
DES_key_schedule *ks, int enc);
void DES_ecb2_encrypt(const_DES_cblock *input, DES_cblock *output,
DES_key_schedule *ks1, DES_key_schedule *ks2, int enc);
void DES_ecb3_encrypt(const_DES_cblock *input, DES_cblock *output,
DES_key_schedule *ks1, DES_key_schedule *ks2,
DES_key_schedule *ks3, int enc);
void DES_ncbc_encrypt(const unsigned char *input, unsigned char *output,
long length, DES_key_schedule *schedule, DES_cblock *ivec,
int enc);
void DES_cfb_encrypt(const unsigned char *in, unsigned char *out,
int numbits, long length, DES_key_schedule *schedule,
DES_cblock *ivec, int enc);
void DES_ofb_encrypt(const unsigned char *in, unsigned char *out,
int numbits, long length, DES_key_schedule *schedule,
DES_cblock *ivec);
void DES_pcbc_encrypt(const unsigned char *input, unsigned char *output,
long length, DES_key_schedule *schedule, DES_cblock *ivec,
int enc);
void DES_cfb64_encrypt(const unsigned char *in, unsigned char *out,
long length, DES_key_schedule *schedule, DES_cblock *ivec,
int *num, int enc);
void DES_ofb64_encrypt(const unsigned char *in, unsigned char *out,
long length, DES_key_schedule *schedule, DES_cblock *ivec,
int *num);
void DES_xcbc_encrypt(const unsigned char *input, unsigned char *output,
long length, DES_key_schedule *schedule, DES_cblock *ivec,
const_DES_cblock *inw, const_DES_cblock *outw, int enc);
void DES_ede2_cbc_encrypt(const unsigned char *input,
unsigned char *output, long length, DES_key_schedule *ks1,
DES_key_schedule *ks2, DES_cblock *ivec, int enc);
void DES_ede2_cfb64_encrypt(const unsigned char *in,
unsigned char *out, long length, DES_key_schedule *ks1,
DES_key_schedule *ks2, DES_cblock *ivec, int *num, int enc);
void DES_ede2_ofb64_encrypt(const unsigned char *in,
unsigned char *out, long length, DES_key_schedule *ks1,
DES_key_schedule *ks2, DES_cblock *ivec, int *num);
void DES_ede3_cbc_encrypt(const unsigned char *input,
unsigned char *output, long length, DES_key_schedule *ks1,
DES_key_schedule *ks2, DES_key_schedule *ks3, DES_cblock *ivec,
int enc);
void DES_ede3_cbcm_encrypt(const unsigned char *in, unsigned char *out,
long length, DES_key_schedule *ks1, DES_key_schedule *ks2,
DES_key_schedule *ks3, DES_cblock *ivec1, DES_cblock *ivec2,
int enc);
void DES_ede3_cfb64_encrypt(const unsigned char *in, unsigned char *out,
long length, DES_key_schedule *ks1, DES_key_schedule *ks2,
DES_key_schedule *ks3, DES_cblock *ivec, int *num, int enc);
void DES_ede3_ofb64_encrypt(const unsigned char *in, unsigned char *out,
long length, DES_key_schedule *ks1,
DES_key_schedule *ks2, DES_key_schedule *ks3,
DES_cblock *ivec, int *num);
DES_LONG DES_cbc_cksum(const unsigned char *input, DES_cblock *output,
long length, DES_key_schedule *schedule,
const_DES_cblock *ivec);
DES_LONG DES_quad_cksum(const unsigned char *input, DES_cblock output[],
long length, int out_count, DES_cblock *seed);
void DES_string_to_key(const char *str, DES_cblock *key);
void DES_string_to_2keys(const char *str, DES_cblock *key1,
DES_cblock *key2);
char *DES_fcrypt(const char *buf, const char *salt, char *ret);
char *DES_crypt(const char *buf, const char *salt);
int DES_enc_read(int fd, void *buf, int len, DES_key_schedule *sched,
DES_cblock *iv);
int DES_enc_write(int fd, const void *buf, int len,
DES_key_schedule *sched, DES_cblock *iv);
```

## Description

This library contains a fast implementation of the DES encryption algorithm.

There are two phases to the use of DES encryption. The first is the generation of a *DES_key_schedule* from a key, the second is the actual encryption. A DES key is of type *DES_cblock*. This type is consists of 8 bytes with odd parity. The least significant bit in each byte is the parity bit. The key schedule is an expanded form of the key; it is used to speed the encryption process.

**DES_random_key()** generates a random key. The PRNG must be seeded prior to using this function (see rand(3)). If the PRNG could not generate a secure key, 0 is returned.

Before a DES key can be used, it must be converted into the architecture dependent *DES_key_schedule* via the **DES_set_key_checked()** or **DES_set_key_unchecked()** function.

**DES_set_key_checked()** will check that the key passed is of odd parity and is not a weak or semi-weak key. If the parity is wrong, then -1 is returned. If the key is a weak key, then -2 is returned. If an error is returned, the key schedule is not generated.

**DES_set_key()** works like **DES_set_key_checked()** if the *DES_check_key* flag is non-zero, otherwise like **DES_set_key_unchecked()**. These functions are available for compatibility; it is recommended to use a function that does not depend on a global variable.

**DES_set_odd_parity()** sets the parity of the passed *key* to odd.

**DES_is_weak_key()** returns 1 if the passed key is a weak key, 0 if it is ok.

The following routines mostly operate on an input and output stream of *DES_cblock*s.

**DES_ecb_encrypt()** is the basic DES encryption routine that encrypts or decrypts a single 8-byte *DES_cblock* in *electronic code book* (ECB) 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 (DES_ENCRYPT), the *input* (cleartext) is encrypted in to the *output* (ciphertext) using the key_schedule specified by the *schedule* argument, previously set via *DES_set_key*. If *encrypt* is zero (DES_DECRYPT), the *input* (now ciphertext) is decrypted into the *output* (now cleartext). Input and output may overlap. **DES_ecb_encrypt()** does not return a value.

**DES_ecb3_encrypt()** encrypts/decrypts the *input* block by using three-key Triple-DES encryption in ECB mode. This involves encrypting the input with *ks1*, decrypting with the key schedule *ks2*, and then encrypting with *ks3*. This routine greatly reduces the chances of brute force breaking of DES and has the advantage of if *ks1*, *ks2* and *ks3* are the same, it is equivalent to just encryption using ECB mode and *ks1* as the key.

The macro **DES_ecb2_encrypt()** is provided to perform two-key Triple-DES encryption by using *ks1* for the final encryption.

**DES_ncbc_encrypt()** encrypts/decrypts using the *cipher-block-chaining* (CBC) mode of DES. If the *encrypt* argument is non-zero, the routine cipher-block-chain encrypts the cleartext data pointed to by the *input* argument into the ciphertext pointed to by the *output* argument, using the key schedule provided by the *schedule* argument, and initialization 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 temporary area and zero filled. The output is always an integral multiple of eight bytes.

**DES_xcbc_encrypt()** is RSA's DESX mode of DES. It uses *inw* and *outw* to 'whiten' the encryption. *inw* and *outw* are secret (unlike the iv) and are as such, part of the key. So the key is sort of 24 bytes. This is much better than CBC DES.

**DES_ede3_cbc_encrypt()** implements outer triple CBC DES encryption with three keys. This means that each DES operation inside the CBC mode is an `"C=E(ks3,D(ks2,E(ks1,M)))"`

. This mode is used by SSL.

The **DES_ede2_cbc_encrypt()** macro implements two-key Triple-DES by reusing *ks1* for the final encryption. `"C=E(ks1,D(ks2,E(ks1,M)))"`

. This form of Triple-DES is used by the RSAREF library.

**DES_pcbc_encrypt()** encrypt/decrypts using the propagating cipher block chaining mode used by Kerberos v4. Its parameters are the same as **DES_ncbc_encrypt()**.

**DES_cfb_encrypt()** encrypt/decrypts using cipher feedback mode. This method takes an array of characters as input and outputs and array of characters. It does not require any padding to 8 character groups. Note: the *ivec* variable is changed and the new changed value needs to be passed to the next call to this function. Since this function runs a complete DES ECB encryption per *numbits*, this function is only suggested for use when sending small numbers of characters.

**DES_cfb64_encrypt()** implements CFB mode of DES with 64bit feedback. Why is this useful you ask? Because this routine will allow you to encrypt an arbitrary number of bytes, no 8 byte padding. Each call to this routine will encrypt the input bytes to output and then update ivec and num. num contains 'how far' we are though ivec. If this does not make much sense, read more about cfb mode of DES :-).

**DES_ede3_cfb64_encrypt()** and **DES_ede2_cfb64_encrypt()** is the same as **DES_cfb64_encrypt()** except that Triple-DES is used.

**DES_ofb_encrypt()** encrypts using output feedback mode. This method takes an array of characters as input and outputs and array of characters. It does not require any padding to 8 character groups. Note: the *ivec* variable is changed and the new changed value needs to be passed to the next call to this function. Since this function runs a complete DES ECB encryption per numbits, this function is only suggested for use when sending small numbers of characters.

**DES_ofb64_encrypt()** is the same as **DES_cfb64_encrypt()** using Output Feed Back mode.

**DES_ede3_ofb64_encrypt()** and **DES_ede2_ofb64_encrypt()** is the same as **DES_ofb64_encrypt()**, using Triple-DES.

The following functions are included in the DES library for compatibility with the MIT Kerberos library.

**DES_cbc_cksum()** produces an 8 byte checksum based on the input stream (via CBC encryption). The last 4 bytes of the checksum are returned and the complete 8 bytes are placed in *output*. This function is used by Kerberos v4. Other applications should use EVP_DigestInit(3) etc. instead.

**DES_quad_cksum()** is a Kerberos v4 function. It returns a 4 byte checksum from the input bytes. The algorithm can be iterated over the input, depending on *out_count*, 1, 2, 3 or 4 times. If *output* is non-NULL, the 8 bytes generated by each pass are written into *output*.

The following are DES-based transformations:

**DES_fcrypt()** is a fast version of the Unix crypt(3) function. This version takes only a small amount of space relative to other fast **crypt()** implementations. This is different to the normal crypt in that the third parameter is the buffer that the return value is written into. It needs to be at least 14 bytes long. This function is thread safe, unlike the normal crypt.

**DES_crypt()** is a faster replacement for the normal system **crypt()**. This function calls **DES_fcrypt()** with a static array passed as the third parameter. This emulates the normal non-thread safe semantics of crypt(3).

**DES_enc_write()** writes *len* bytes to file descriptor *fd* from buffer *buf*. The data is encrypted via *pcbc_encrypt* (default) using *sched* for the key and *iv* as a starting vector. The actual data send down *fd* consists of 4 bytes (in network byte order) containing the length of the following encrypted data. The encrypted data then follows, padded with random data out to a multiple of 8 bytes.

**DES_enc_read()** is used to read *len* bytes from file descriptor *fd* into buffer *buf*. The data being read from *fd* is assumed to have come from **DES_enc_write()** and is decrypted using *sched* for the key schedule and *iv* for the initial vector.

**Warning:** The data format used by **DES_enc_write()** and **DES_enc_read()** has a cryptographic weakness: When asked to write more than MAXWRITE bytes, **DES_enc_write()** will split the data into several chunks that are all encrypted using the same IV. So don't use these functions unless you are sure you know what you do (in which case you might not want to use them anyway). They cannot handle non-blocking sockets. **DES_enc_read()** uses an internal state and thus cannot be used on multiple files.

*DES_rw_mode* is used to specify the encryption mode to use with **DES_enc_read()** and **DES_end_write()**. If set to *DES_PCBC_MODE* (the default), DES_pcbc_encrypt is used. If set to *DES_CBC_MODE* DES_cbc_encrypt is used.

## Notes

Single-key DES is insecure due to its short key size. ECB mode is not suitable for most applications; see des_modes(7).

The evp(3) library provides higher-level encryption functions.

## Bugs

**DES_3cbc_encrypt()** is flawed and must not be used in applications.

**DES_cbc_encrypt()** does not modify **ivec**; use **DES_ncbc_encrypt()** instead.

**DES_cfb_encrypt()** and **DES_ofb_encrypt()** operates on input of 8 bits. What this means is that if you set numbits to 12, and length to 2, the first 12 bits will come from the 1st input byte and the low half of the second input byte. The second 12 bits will have the low 8 bits taken from the 3rd input byte and the top 4 bits taken from the 4th input byte. The same holds for output. This function has been implemented this way because most people will be using a multiple of 8 and because once you get into pulling bytes input bytes apart things get ugly!

**DES_string_to_key()** is available for backward compatibility with the MIT library. New applications should use a cryptographic hash function. The same applies for **DES_string_to_2key()**.

## Conforming to

ANSI X3.106

The **des** library was written to be source code compatible with the MIT Kerberos library.

## See Also

## History

In OpenSSL 0.9.7, all des_ functions were renamed to DES_ to avoid clashes with older versions of libdes. Compatibility des_ functions are provided for a short while, as well as **crypt()**. Declarations for these are in <openssl/des_old.h>. There is no DES_ variant for **des_random_seed()**. This will happen to other functions as well if they are deemed redundant (**des_random_seed()** just calls **RAND_seed()** and is present for backward compatibility only), buggy or already scheduled for removal.

**des_cbc_cksum()**, **des_cbc_encrypt()**, **des_ecb_encrypt()**, **des_is_weak_key()**, **des_key_sched()**, **des_pcbc_encrypt()**, **des_quad_cksum()**, **des_random_key()** and **des_string_to_key()** are available in the MIT Kerberos library; **des_check_key_parity()**, **des_fixup_key_parity()** and **des_is_weak_key()** are available in newer versions of that library.

**des_set_key_checked()** and **des_set_key_unchecked()** were added in OpenSSL 0.9.5.

**des_generate_random_block()**, **des_init_random_number_generator()**, **des_new_random_key()**, **des_set_random_generator_seed()** and **des_set_sequence_number()** and **des_rand_data()** are used in newer versions of Kerberos but are not implemented here.

**des_random_key()** generated cryptographically weak random data in SSLeay and in OpenSSL prior version 0.9.5, as well as in the original MIT library.

## Author

Eric Young (eay@cryptsoft.com). Modified for the OpenSSL project (http://www.openssl.org).