ENC

Section: OpenSSL (1)
Updated: 2020-07-28
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NAME

openssl-enc, enc - symmetric cipher routines

SYNOPSIS

openssl enc -cipher [-help] [-list] [-ciphers] [-in filename] [-out filename] [-pass arg] [-e] [-d] [-a] [-base64] [-A] [-k password] [-kfile filename] [-K key] [-iv IV] [-S salt] [-salt] [-nosalt] [-z] [-md digest] [-iter count] [-pbkdf2] [-p] [-P] [-bufsize number] [-nopad] [-debug] [-none] [-rand file...] [-writerand file] [-engine id]

openssl [cipher] [...]

DESCRIPTION

The symmetric cipher commands allow data to be encrypted or decrypted using various block and stream ciphers using keys based on passwords or explicitly provided. Base64 encoding or decoding can also be performed either by itself or in addition to the encryption or decryption.

OPTIONS

-help: Print out a usage message.
-list: List all supported ciphers.
-ciphers: Alias of -list to display all supported ciphers.
-in filename: The input filename, standard input by default.
-out filename: The output filename, standard output by default.
-pass arg: The password source. For more information about the format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
-e: Encrypt the input data: this is the default.
-d: Decrypt the input data.
-a: Base64 process the data. This means that if encryption is taking place the data is base64 encoded after encryption. If decryption is set then the input data is base64 decoded before being decrypted.
-base64: Same as -a
-A: If the -a option is set then base64 process the data on one line.
-k password: The password to derive the key from. This is for compatibility with previous versions of OpenSSL. Superseded by the -pass argument.
-kfile filename: Read the password to derive the key from the first line of filename. This is for compatibility with previous versions of OpenSSL. Superseded by the -pass argument.
-md digest: Use the specified digest to create the key from the passphrase. The default algorithm is sha-256.
-iter count: Use a given number of iterations on the password in deriving the encryption key. High values increase the time required to brute-force the resulting file. This option enables the use of PBKDF2 algorithm to derive the key.
-pbkdf2: Use PBKDF2 algorithm with default iteration count unless otherwise specified.
-nosalt: Don't use a salt in the key derivation routines. This option SHOULD NOT be used except for test purposes or compatibility with ancient versions of OpenSSL.
-salt: Use salt (randomly generated or provide with -S option) when encrypting, this is the default.
-S salt: The actual salt to use: this must be represented as a string of hex digits.
-K key: The actual key to use: this must be represented as a string comprised only of hex digits. If only the key is specified, the IV must additionally specified using the -iv option. When both a key and a password are specified, the key given with the -K option will be used and the IV generated from the password will be taken. It does not make much sense to specify both key and password.
-iv IV: The actual IV to use: this must be represented as a string comprised only of hex digits. When only the key is specified using the -K option, the IV must explicitly be defined. When a password is being specified using one of the other options, the IV is generated from this password.
-p: Print out the key and IV used.
-P: Print out the key and IV used then immediately exit: don't do any encryption or decryption.
-bufsize number: Set the buffer size for I/O.
-nopad: Disable standard block padding.
-debug: Debug the BIOs used for I/O.
-z: Compress or decompress clear text using zlib before encryption or after decryption. This option exists only if OpenSSL with compiled with zlib or zlib-dynamic option.
-none: Use NULL cipher (no encryption or decryption of input).
-rand file...: A file or files containing random data used to seed the random number generator. Multiple files can be specified separated by an OS-dependent character. The separator is ; for MS-Windows, , for OpenVMS, and : for all others.
[-writerand file]: Writes random data to the specified file upon exit. This can be used with a subsequent -rand flag.

NOTES

The program can be called either as openssl cipher or openssl enc -cipher. The first form doesn't work with engine-provided ciphers, because this form is processed before the configuration file is read and any ENGINEs loaded. Use the list command to get a list of supported ciphers.

Engines which provide entirely new encryption algorithms (such as the ccgost engine which provides gost89 algorithm) should be configured in the configuration file. Engines specified on the command line using -engine options can only be used for hardware-assisted implementations of ciphers which are supported by the OpenSSL core or another engine specified in the configuration file.

When the enc command lists supported ciphers, ciphers provided by engines, specified in the configuration files are listed too.

A password will be prompted for to derive the key and IV if necessary.

The -salt option should ALWAYS be used if the key is being derived from a password unless you want compatibility with previous versions of OpenSSL.

Without the -salt option it is possible to perform efficient dictionary attacks on the password and to attack stream cipher encrypted data. The reason for this is that without the salt the same password always generates the same encryption key. When the salt is being used the first eight bytes of the encrypted data are reserved for the salt: it is generated at random when encrypting a file and read from the encrypted file when it is decrypted.

Some of the ciphers do not have large keys and others have security implications if not used correctly. A beginner is advised to just use a strong block cipher, such as AES, in CBC mode.

All the block ciphers normally use PKCS#5 padding, also known as standard block padding. This allows a rudimentary integrity or password check to be performed. However since the chance of random data passing the test is better than 1 in 256 it isn't a very good test.

If padding is disabled then the input data must be a multiple of the cipher block length.

All RC2 ciphers have the same key and effective key length.

Blowfish and RC5 algorithms use a 128 bit key.

SUPPORTED CIPHERS

Note that some of these ciphers can be disabled at compile time and some are available only if an appropriate engine is configured in the configuration file. The output of the enc command run with the -ciphers option (that is openssl enc -ciphers) produces a list of ciphers, supported by your version of OpenSSL, including ones provided by configured engines.

The enc program does not support authenticated encryption modes like CCM and GCM, and will not support such modes in the future. The enc interface by necessity must begin streaming output (e.g., to standard output when -out is not used) before the authentication tag could be validated, leading to the usage of enc in pipelines that begin processing untrusted data and are not capable of rolling back upon authentication failure. The AEAD modes currently in common use also suffer from catastrophic failure of confidentiality and/or integrity upon reuse of key/iv/nonce, and since enc places the entire burden of key/iv/nonce management upon the user, the risk of exposing AEAD modes is too great to allow. These key/iv/nonce management issues also affect other modes currently exposed in enc, but the failure modes are less extreme in these cases, and the functionality cannot be removed with a stable release branch. For bulk encryption of data, whether using authenticated encryption modes or other modes, cms(1) is recommended, as it provides a standard data format and performs the needed key/iv/nonce management.

 base64             Base 64

 bf-cbc             Blowfish in CBC mode
 bf                 Alias for bf-cbc
 blowfish           Alias for bf-cbc
 bf-cfb             Blowfish in CFB mode
 bf-ecb             Blowfish in ECB mode
 bf-ofb             Blowfish in OFB mode

 cast-cbc           CAST in CBC mode
 cast               Alias for cast-cbc
 cast5-cbc          CAST5 in CBC mode
 cast5-cfb          CAST5 in CFB mode
 cast5-ecb          CAST5 in ECB mode
 cast5-ofb          CAST5 in OFB mode

 chacha20           ChaCha20 algorithm

 des-cbc            DES in CBC mode
 des                Alias for des-cbc
 des-cfb            DES in CFB mode
 des-ofb            DES in OFB mode
 des-ecb            DES in ECB mode

 des-ede-cbc        Two key triple DES EDE in CBC mode
 des-ede            Two key triple DES EDE in ECB mode
 des-ede-cfb        Two key triple DES EDE in CFB mode
 des-ede-ofb        Two key triple DES EDE in OFB mode

 des-ede3-cbc       Three key triple DES EDE in CBC mode
 des-ede3           Three key triple DES EDE in ECB mode
 des3               Alias for des-ede3-cbc
 des-ede3-cfb       Three key triple DES EDE CFB mode
 des-ede3-ofb       Three key triple DES EDE in OFB mode

 desx               DESX algorithm.

 gost89             GOST 28147-89 in CFB mode (provided by ccgost engine)
 gost89-cnt        `GOST 28147-89 in CNT mode (provided by ccgost engine)

 idea-cbc           IDEA algorithm in CBC mode
 idea               same as idea-cbc
 idea-cfb           IDEA in CFB mode
 idea-ecb           IDEA in ECB mode
 idea-ofb           IDEA in OFB mode

 rc2-cbc            128 bit RC2 in CBC mode
 rc2                Alias for rc2-cbc
 rc2-cfb            128 bit RC2 in CFB mode
 rc2-ecb            128 bit RC2 in ECB mode
 rc2-ofb            128 bit RC2 in OFB mode
 rc2-64-cbc         64 bit RC2 in CBC mode
 rc2-40-cbc         40 bit RC2 in CBC mode

 rc4                128 bit RC4
 rc4-64             64 bit RC4
 rc4-40             40 bit RC4

 rc5-cbc            RC5 cipher in CBC mode
 rc5                Alias for rc5-cbc
 rc5-cfb            RC5 cipher in CFB mode
 rc5-ecb            RC5 cipher in ECB mode
 rc5-ofb            RC5 cipher in OFB mode

 seed-cbc           SEED cipher in CBC mode
 seed               Alias for seed-cbc
 seed-cfb           SEED cipher in CFB mode
 seed-ecb           SEED cipher in ECB mode
 seed-ofb           SEED cipher in OFB mode

 sm4-cbc            SM4 cipher in CBC mode
 sm4                Alias for sm4-cbc
 sm4-cfb            SM4 cipher in CFB mode
 sm4-ctr            SM4 cipher in CTR mode
 sm4-ecb            SM4 cipher in ECB mode
 sm4-ofb            SM4 cipher in OFB mode

 aes-[128|192|256]-cbc  128/192/256 bit AES in CBC mode
 aes[128|192|256]       Alias for aes-[128|192|256]-cbc
 aes-[128|192|256]-cfb  128/192/256 bit AES in 128 bit CFB mode
 aes-[128|192|256]-cfb1 128/192/256 bit AES in 1 bit CFB mode
 aes-[128|192|256]-cfb8 128/192/256 bit AES in 8 bit CFB mode
 aes-[128|192|256]-ctr  128/192/256 bit AES in CTR mode
 aes-[128|192|256]-ecb  128/192/256 bit AES in ECB mode
 aes-[128|192|256]-ofb  128/192/256 bit AES in OFB mode

 aria-[128|192|256]-cbc  128/192/256 bit ARIA in CBC mode
 aria[128|192|256]       Alias for aria-[128|192|256]-cbc
 aria-[128|192|256]-cfb  128/192/256 bit ARIA in 128 bit CFB mode
 aria-[128|192|256]-cfb1 128/192/256 bit ARIA in 1 bit CFB mode
 aria-[128|192|256]-cfb8 128/192/256 bit ARIA in 8 bit CFB mode
 aria-[128|192|256]-ctr  128/192/256 bit ARIA in CTR mode
 aria-[128|192|256]-ecb  128/192/256 bit ARIA in ECB mode
 aria-[128|192|256]-ofb  128/192/256 bit ARIA in OFB mode

 camellia-[128|192|256]-cbc  128/192/256 bit Camellia in CBC mode
 camellia[128|192|256]       Alias for camellia-[128|192|256]-cbc
 camellia-[128|192|256]-cfb  128/192/256 bit Camellia in 128 bit CFB mode
 camellia-[128|192|256]-cfb1 128/192/256 bit Camellia in 1 bit CFB mode
 camellia-[128|192|256]-cfb8 128/192/256 bit Camellia in 8 bit CFB mode
 camellia-[128|192|256]-ctr  128/192/256 bit Camellia in CTR mode
 camellia-[128|192|256]-ecb  128/192/256 bit Camellia in ECB mode
 camellia-[128|192|256]-ofb  128/192/256 bit Camellia in OFB mode

EXAMPLES

Just base64 encode a binary file:

 openssl base64 -in file.bin -out file.b64

Decode the same file

 openssl base64 -d -in file.b64 -out file.bin

Encrypt a file using AES-128 using a prompted password and PBKDF2 key derivation:

 openssl enc -aes128 -pbkdf2 -in file.txt -out file.aes128

Decrypt a file using a supplied password:

 openssl enc -aes128 -pbkdf2 -d -in file.aes128 -out file.txt \
    -pass pass:<password>

Encrypt a file then base64 encode it (so it can be sent via mail for example) using AES-256 in CTR mode and PBKDF2 key derivation:

 openssl enc -aes-256-ctr -pbkdf2 -a -in file.txt -out file.aes256

Base64 decode a file then decrypt it using a password supplied in a file:

 openssl enc -aes-256-ctr -pbkdf2 -d -a -in file.aes256 -out file.txt \
    -pass file:<passfile>

BUGS

The -A option when used with large files doesn't work properly.

The enc program only supports a fixed number of algorithms with certain parameters. So if, for example, you want to use RC2 with a 76 bit key or RC4 with an 84 bit key you can't use this program.

HISTORY

The default digest was changed from MD5 to SHA256 in OpenSSL 1.1.0.

The -list option was added in OpenSSL 1.1.1e.

COPYRIGHT

Licensed under the OpenSSL license (the ``License''). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.