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# - Unix, Linux Command

# NAME

enc - symmetric cipher routines

# SYNOPSIS

openssl enc -ciphername [-in filename] [-out filename] [-pass arg] [-e] [-d] [-a] [-A] [-k password] [-kfile filename] [-K key] [-iv IV] [-p] [-P] [-bufsize number] [-nopad] [-debug]

# 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

Tag | Description
--- | ---
-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 option should ALWAYS be used unless compatibility with previous versions of OpenSSL or SSLeay is required. This option is only present on OpenSSL versions 0.9.5 or above.
-nosalt | don’t use a salt in the key derivation routines. This is the default for compatibility with previous 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.
-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 Superseded by the -pass argument.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 Superseded by the -pass argument.
-S salt | the actual salt to use: this must be represented as a string comprised only 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.

# NOTES

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

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

`

     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.

``

     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.

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