- Unix Commands Reference
- Unix - Tutorial Home
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
- Unix, Linux Command
NAMEenc - symmetric cipher routines
SYNOPSISopenssl 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]
DESCRIPTIONThe 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.
|-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||dont 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 Superseded by the -pass argument.|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 Superseded by the -pass argument.|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: dont 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.|
NOTESThe 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 isnt 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.
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
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
The -A option when used with large files doesnt 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 cant use this program.