DES_SET_KEY(3)

💅 DES_SET_KEY(3) 💅

Okay bestie, welcome to the DES_SET_KEY(3) page from the Library Functions Manual. This is the DES encryption page, and it is not just one function — it is a whole ensemble cast. Think main-character energy, but for an entire header file. 🎀

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✨ NAME ✨

The full lineup, no cap: 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 encryption.

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🦋 SYNOPSIS 🦋

Here is the synopsis block exactly as the page gives it — library line, include, and every single prototype. Do not let the wall of signatures scare you; it is just the DES friend group saying hi. 😭✨

       library “libcrypto” #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);

✨ DESCRIPTION ✨

Okay so this library is literally a fast implementation of the DES encryption algorithm. Like, speed is the whole vibe. 🏎️

There are two phases to using DES encryption, bestie, and you gotta know both:

1. Generating a DES_key_schedule from a key.
2. The actual encryption.

A DES key is of type DES_cblock. This type consists of 8 bytes with odd parity, and the least significant bit in each byte is the parity bit. The key schedule is an expanded form of the key — it's used to speed up the encryption process, and it's giving "prep work that pays off later" energy. 💅

DES_random_key() generates a random key in odd parity. Random is the moment, fr fr. 🎲

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. The way this works:

• 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. No schedule for you. 🙅‍♀️

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. Global variables are so not the main character here. 😬

DES_set_odd_parity() sets the parity of the passed key to odd. Little glow-up for your key. ✨

The following routines mostly operate on an input and output stream of DES_cblocks.

🦋 The ECB girlies

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. Here's the tea:

• If the enc argument is non-zero (DES_ENCRYPT), the input (cleartext) is encrypted into the output (ciphertext) using the key_schedule specified by the schedule argument, previously set via DES_set_key().
• If enc is zero (DES_DECRYPT), the input (now ciphertext) is decrypted into the output (now cleartext).

Input and output may overlap — they can literally be the same memory and it's fine, no drama. 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. Iconic shortcut behavior. 🔥

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

🌸 CBC mode (the chunky one)

DES_ncbc_encrypt() encrypts/decrypts using the cipher-block-chaining (CBC) mode of DES. If the enc 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. No half-blocks, we don't do that here. 💅

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 — highkey an upgrade. 🫶

DES_ede3_cbc_encrypt() implements outer triple CBC DES encryption with three keys. This means that each DES operation inside the CBC mode is "C=E(ks3,D(ks2,E(ks1,M)))". This mode is used by SSL. Yes, that 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() encrypts/decrypts using the propagating cipher block chaining mode used by Kerberos v4. Its parameters are the same as DES_ncbc_encrypt(). Same cast, different plot. 🎭

🧚 Feedback modes go brrr

DES_cfb_encrypt() encrypts/decrypts using cipher feedback mode. This method takes an array of characters as input and outputs an array of characters. It does not require any padding to 8 character groups — no padding, no problem.

Note: the ivec variable is changed and the new changed value needs to be passed to the next call to this function. Don't forget, or the whole thing just falls apart, bestie. 😭

Since this function runs a complete DES ECB encryption per numbits, this function is only suggested for use when sending a small number of characters. Small batches only, she's not built for volume.

DES_cfb64_encrypt() implements CFB mode of DES with 64-bit feedback. Why is this useful you ask? Because this routine will allow you to encrypt an arbitrary number of bytes, without 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. (iykyk 🫶)

The DES_ede3_cfb64_encrypt() function and the DES_ede2_cfb64_encrypt() macro are 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 an 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. Again! Pass it along, bestie. 🎀

Since this function runs a complete DES ECB encryption per numbits, this function is only suggested for use when sending a small number of characters.

DES_ofb64_encrypt() is the same as DES_cfb64_encrypt() using Output Feed Back mode. Literally same energy, different mode name.

The DES_ede3_ofb64_encrypt() function and the DES_ede2_ofb64_encrypt() macro are the same as DES_ofb64_encrypt(), using Triple-DES.

💜 MIT Kerberos compatibility corner

The following functions are included in the DES library for compatibility with the MIT Kerberos library. They're giving "old friend who's still on the group chat." 👵

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. Like, respectfully, use the modern thing. 🙈

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. The salt must be two ASCII characters. This version is different from 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. The fourteenth byte is set to NUL. This version takes only a small amount of space relative to other fast crypt implementations. It is thread safe, unlike the normal crypt. She's fast, she's compact, she's safe — the full package. 💅✨

DES_crypt() is a faster replacement for the normal system crypt(3). 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). So yeah, it's faster but it inherited the family's non-thread-safe baggage. 💀

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💖 RETURN VALUES 💖

• DES_set_key(), DES_key_sched(), and DES_set_key_checked() return 0 on success or a negative value on error.
• DES_is_weak_key() returns 1 if the passed key is a weak key or 0 if it is ok.
• DES_cbc_cksum() and DES_quad_cksum() return a 4-byte integer representing the last 4 bytes of the checksum of the input.
• DES_fcrypt() returns a pointer to the caller-provided buffer ret, and DES_crypt() returns a pointer to a static buffer. Both are allowed to return NULL to indicate failure, but currently, they cannot fail. (Famous last words, but okay 😭)

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🌈 SEE ALSO 🌈

crypt(3), EVP_des_cbc(3), EVP_EncryptInit(3)

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👑 STANDARDS 👑

ANSI X3.106

The DES library was initially written to be source code compatible with the MIT Kerberos library. Respect where it's due. 🫡

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🎀 HISTORY 🎀

Okay so the lore is long, buckle up:

• DES_random_key(), DES_set_key(), DES_key_sched(), DES_set_odd_parity(), DES_is_weak_key(), DES_ecb_encrypt(), DES_cfb_encrypt(), DES_ofb_encrypt(), DES_pcbc_encrypt(), DES_cfb64_encrypt(), DES_ofb64_encrypt(), DES_ede3_cbc_encrypt(), DES_cbc_cksum(), DES_quad_cksum(), DES_string_to_key(), DES_string_to_2keys(), and DES_crypt() appeared in SSLeay 0.4 or earlier.
• DES_ncbc_encrypt() first appeared in SSLeay 0.4.2.
• DES_ede2_cbc_encrypt() first appeared in SSLeay 0.4.4.
• DES_ecb2_encrypt(), DES_ecb3_encrypt(), DES_ede2_cfb64_encrypt(), DES_ede2_ofb64_encrypt(), DES_ede3_cfb64_encrypt(), and DES_ede3_ofb64_encrypt() first appeared in SSLeay 0.5.1.
• DES_xcbc_encrypt() first appeared in SSLeay 0.6.2.
• DES_fcrypt() first appeared in SSLeay 0.6.5.

These functions have been available since OpenBSD 2.4.

DES_set_key_checked() and DES_set_key_unchecked() first appeared in OpenSSL 0.9.5 and have been available since OpenBSD 2.7.

In OpenSSL 0.9.7 and OpenBSD 3.2, all des_ functions were renamed to DES_ to avoid clashes with older versions of libdes. The glow-up rebrand era. 💅

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🌸 AUTHORS 🌸

Eric Young <eay@cryptsoft.com>

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⚠️ CAVEATS ⚠️

Single-key DES is insecure due to its short key size. ECB mode is not suitable for most applications. Like, do not use this for anything that needs to actually be secure, bestie. I'm begging. 🚨

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💀 BUGS 💀

DES_cbc_encrypt does not modify ivec; use DES_ncbc_encrypt() instead. Noted. Fix your call. 📝

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 input bytes apart things get ugly! 😭 Fr fr, bit-slicing by hand is not the vibe.

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(). Old functions, new apps should move on. 🕊️

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That's the whole page, bestie — slay. 💅✨ This was DES_SET_KEY(3) from the Debian build, dated June 8, 2025. Go forth and encrypt responsibly (or, like, don't use single DES at all — see CAVEATS 🫶).