openssl-enc, enc - symmetric cipher routines
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] [...]
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.
- Print out a usage message.
- List all supported 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 "Pass Phrase Options" in openssl(1).
- Encrypt the input data: this is the default.
- Decrypt the input data.
- 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.
- Same as -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 Superseded by the -pass argument.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 Superseded by the -pass argument.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.
- Use PBKDF2 algorithm with default iteration count unless otherwise specified.
- 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.
- 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.
- Print out the key and IV used.
- 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.
- Disable standard block padding.
- Debug the BIOs used for I/O.
- Compress or decompress encrypted data using zlib after encryption or before decryption. This option exists only if OpenSSL was compiled with the zlib or zlib-dynamic option.
- 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.
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.
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
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>
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.
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 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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.