A beginner is advised to just use a strong blockĪll the block ciphers normally use PKCS#5 padding also known as standard block padding: this allows a rudimentary integrity or password check to be Some of the ciphers do not have large keys and others have security implications if not used correctly. When the salt is being used the first eight bytes of theĮncrypted 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. Reason for this is that without the salt the same password always generates the same encryption key. Without the -salt option it is possible to perform efficient dictionary attacks on the password and to attack stream cipher encrypted data. The -salt option should ALWAYS be used if the key is being derived from a password unless you want compatibility with previous When enc command lists supported ciphers, ciphers provided by engines, specified in the configuration files are listed too.Ī password will be prompted for to derive the key and IV if necessary. OpenSSL core or other engine, specified 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 But the first form doesn't work with engine-providedĬiphers, because this form is processed before the configuration file is read and any ENGINEs loaded.Įngines which provide entirely new encryption algorithms (such as ccgost engine which provides gost89 algorithm) should be configured in the configurationįile. The program can be called either as openssl ciphername or openssl enc -ciphername. none Use NULL cipher (no encryption or decryption of input). This option exists only if OpenSSL with compiled with zlib or bufsize number set the buffer size for I/OĬompress or decompress clear text using zlib before encryption or after decryption. Print out the key and IV used then immediately exit: don't do any encryption or decryption. When a password is being specified using one of the other options, the IV is generated Option, the IV must explicitly be defined. When only the key is specified using the -K iv IV the actual IV to use: this must be represented as a string comprised only of hex digits. It probably does not make much sense to specify both key and password. IV generated from the password will be taken. When both a key and a password are specified, the key given with the -K option will be used and the If only the key is specified, the IV mustĪdditionally specified using the -iv option. K key the actual key to use: this must be represented as a string comprised only of hex digits. S salt the actual salt to use: this must be represented as a string of hex digits. salt use salt (randomly generated or provide with -S option) when encrypting (this is the default). This is for compatibility with previous versions of OpenSSL. kfile filename read the password to derive the key from the first line of filename. k password the password to derive the key from. If the -a option is set then base64 process the data on one line. Is base64 decoded before being decrypted. This means that if encryption is taking place the data is base64 encoded after encryption. This option SHOULD NOT be used except for test purposes or compatibility with ancientĮncrypt the input data: this is the default.īase64 process the data. nosalt don't use a salt in the key derivation routines. salt use a salt in the key derivation routines. For more information about the format of arg see the PASS PHRASE ARGUMENTS section in out filename the output filename, standard output by default. in filename the input filename, standard input by default. Base64 encoding or decoding can also be performed either by itself or in addition to the encryption or decryption. The symmetric cipher commands allow data to be encrypted or decrypted using various block and stream ciphers using keys based on passwords or explicitly
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