Decipher
The decipher command-line utility converts ciphertext to plaintext.
Example Usage
We list a few examples of the decipher command here to illustrate its usefulness and ease of use. To get started, lets decypt a text file:
decipher README.cip README.txt
Here Alice wands to decipher a secret message from Bob. Alice knows Bob's secret passphrase and has a copy of his private keyring. To restore the original message content, Alice uses this command:
decipher -keyring ./keyring.xdm secret-message.cip message.txt
To ensure your ciphertext is not easily revealed, the decipher program takes these precautions:
Passphrase
If your command line does not include the -passphrase filename option, the passphrase is interactively requested and has a maximum length of 4096 characters and symbols. The phrase can be virtually unlimited if obtained from a file. Try to make your passphrases long and unpredictable.
Keyring
Your secret key is stored in a private keyring. If you lose your keyring, it is impossible to restore your original message content.
Entropy
If the decipher program appears to halt it may be waiting for your system to generate entropy. Move your mouse or press keystrokes in another window. Once enough entropy is generated, the decipher program will complete.
Exceptions
If simple mistakes are made, an exception message is displayed. For example if you use '-cpher' instead of '-cipher', decipher complains. However, if anything goes wrong inside the decipher engine, the program exits with a simple status code. This precaution is to prevent information leaks about the decipher process.
Option Summary
The decipher command recognizes these options. Click on an option to get more details about how that option works.
| Option | Description |
|---|---|
| -authenticate method | authenticate with this method: Secret or Public |
| -chunksize bytes | number of bytes in a chunk |
| -cipher type | cipher to decrypt content |
| -(de)compress | automagically (de)compress BZIP and ZIP files |
| -debug events | display copious debugging information |
| -entropy type | increase content entropy |
| -help | print program options |
| -hmac hash | ensure message integrity with this hash |
| -key hash | strengthen the key with this hash |
| -key-length value | cipher key length in bits: 256, 512, 1024, or 2048 |
| -keyring filename | add the private key to this keyring |
| -level value | entropy level: 1 (less entropy) to 9 (more entropy) |
| -list type | print a list of supported option arguments |
| -log format | format of debugging information |
| -mode type | mode of decryption |
| -passphrase filename | get the passphrase from this file |
| -properties filename | cipher properties to/from this file |
| -random hash | strengthen random data with this hash |
| -true-random | strengthen deciphering with true random numbers |
| -verbose | print detailed information about the secure content |
| -version | print version information |