When you encrypt a file, the original file is not removed or changed. The output file is encrypted.
For solutions to common errors from the encrypt command, see the section that follows the examples.
Create a symmetric key of the appropriate length.
You have two options. You can provide a passphrase from which a key will be generated. Or you can provide a key.
If you provide a passphrase, you must store or remember the passphrase. If you store the passphrase online, the passphrase file should be readable only by you.
If you provide a key, it must be the correct size for the mechanism. For the procedure, see How to Generate a Symmetric Key by Using the dd Command.
Provide a key and use a symmetric key algorithm with the encrypt command.
% encrypt -a algorithm [ -k keyfile ] -i input-file -o output-file |
Is the algorithm to use to encrypt the file. Type the algorithm as the algorithm appears in the output of the encrypt -l command.
Is the file that contains a key of algorithm-specified length. The key length for each algorithm is listed, in bits, in the output of the encrypt -l command.
Is the input file that you want to encrypt. This file is left unchanged by the command.
Is the output file that is the encrypted form of the input file.
In the following example, a file is encrypted with the AES algorithm. The key is generated from the passphrase. If the passphrase is stored in a file, the file should not be readable by anyone but the user.
% encrypt -a aes -i ticket.to.ride -o ~/enc/e.ticket.to.ride Enter passphrase: <Type passphrase> Re-enter passphrase: Type passphrase again |
The input file, ticket.to.ride, still exists in its original form.
To decrypt the output file, the user uses the same passphrase and encryption mechanism that encrypted the file.
% decrypt -a aes -i ~/enc/e.ticket.to.ride -o ~/d.ticket.to.ride Enter passphrase: <Type passphrase> |
In the following example, a file is encrypted with the AES algorithm. AES mechanisms use a key of 128 bits, or 16 bytes.
% encrypt -a aes -k ~/keyf/05.07.aes16 \ -i ticket.to.ride -o ~/enc/e.ticket.to.ride |
The input file, ticket.to.ride, still exists in its original form.
To decrypt the output file, the user uses the same key and encryption mechanism that encrypted the file.
% decrypt -a aes -k ~/keyf/05.07.aes16 \ -i ~/enc/e.ticket.to.ride -o ~/d.ticket.to.ride |
In the following example, a file is encrypted with the ARCFOUR algorithm. The ARCFOUR algorithm accepts a key of 8 bits (1 byte), 64 bits (8 bytes), or 128 bits (16 bytes).
% encrypt -a arcfour -i personal.txt \ -k ~/keyf/05.07.rc4.8 -o ~/enc/e.personal.txt |
To decrypt the output file, the user uses the same key and encryption mechanism that encrypted the file.
% decrypt -a arcfour -i ~/enc/e.personal.txt \ -k ~/keyf/05.07.rc4.8 -o ~/personal.txt |
In the following example, a file is encrypted with the 3DES algorithm. The 3DES algorithm requires a key of 192 bits, or 24 bytes.
% encrypt -a 3des -k ~/keyf/05.07.des24 \ -i ~/personal2.txt -o ~/enc/e.personal2.txt |
To decrypt the output file, the user uses the same key and encryption mechanism that encrypted the file.
% decrypt -a 3des -k ~/keyf/05.07.des24 \ -i ~/enc/e.personal2.txt -o ~/personal2.txt |
The following messages indicate that the key that you provided to the encrypt command is not permitted by the algorithm that you are using.
encrypt: unable to create key for crypto operation: CKR_ATTRIBUTE_VALUE_INVALID
encrypt: failed to initialize crypto operation: CKR_KEY_SIZE_RANGE
If you pass a key that does not meet the requirements of the algorithm, you must supply a better key.
One option is to use a passphrase. The framework then provides a key that meets the requirements.
The second option is to pass a key size that the algorithm accepts. For example, the DES algorithm requires a key of 64 bits. The 3DES algorithm requires a key of 192 bits.