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ENC

Section: OpenSSL (1SSL)

Updated: 2014-10-15

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NAME

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 Superseded by the -pass argument.: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 Superseded by the -pass argument.: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.

EXAMPLES

Just base64 encode a binary file:

Decode the same file

Encrypt a file using triple DES in CBC mode using a prompted password:

Decrypt a file using a supplied password:

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

Base64 decode a file then decrypt it:

Decrypt some data using a supplied 40 bit RC4 key:

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.


Index

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

NOTES

SUPPORTED CIPHERS

EXAMPLES

BUGS


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