ENC

Section: OpenSSL (1)
Updated: 2019-02-26
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NAME

openssl-enc, enc - symmetric cipher routines

SYNOPSIS

openssl enc -ciphername [-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] [-p] [-P] [-bufsize number] [-nopad] [-debug] [-none] [-engine id]

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

-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).
-salt: use a salt in the key derivation routines. This is the default.
-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 and SSLeay.
-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 Superseded by the -pass argument.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 Superseded by the -pass argument.
-nosalt: do not use a salt
-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 probably 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).

NOTES

The program can be called either as openssl ciphername or openssl enc -ciphername. But 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.

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

When 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 and SSLeay.

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 in CBC mode such as bf or des3.

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 unsupported options (for example openssl enc -help) includes a list of ciphers, supported by your versesion of OpenSSL, including ones provided by configured engines.

The enc program does not support authenticated encryption modes like CCM and GCM. The utility does not store or retrieve the authentication tag.

 base64             Base 64

 bf-cbc             Blowfish in CBC mode
 bf                 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

 des-cbc            DES in CBC mode
 des                Alias for des-cbc
 des-cfb            DES in CBC 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

 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]-ecb  128/192/256 bit AES in ECB mode
 aes-[128|192|256]-ofb  128/192/256 bit AES 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 triple DES in CBC mode using a prompted password:

 openssl des3 -salt -in file.txt -out file.des3

Decrypt a file using a supplied password:

 openssl des3 -d -salt -in file.des3 -out file.txt -k mypassword

Encrypt a file then base64 encode it (so it can be sent via mail for example) using Blowfish in CBC mode:

 openssl bf -a -salt -in file.txt -out file.bf

Base64 decode a file then decrypt it:

 openssl bf -d -salt -a -in file.bf -out file.txt

Decrypt some data using a supplied 40 bit RC4 key:

 openssl rc4-40 -in file.rc4 -out file.txt -K 0102030405

BUGS

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

There should be an option to allow an iteration count to be included.

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.