openssl command-line program

The openssl command can be used to create digests of a file, which can be used to verify that a file has not been tampered with:

$ echo "test file"> foo.txt

$ openssl dgst -md5 foo.txt

MD5(foo.txt)= b05403212c66bdc8ccc597fedf6cd5fe

$ openssl dgst -sha1 foo.txt

SHA1(foo.txt)= 0181d93fee60b818e3f92e470ea97a2aff4ca56a

To view the other message digests that can be used, look at the output of openssl list-message-digest-commands.

You can also use openssl to encrypt files. To view the list of available ciphers, use openssl list-cipher-commands. Once you’ve chosen a cipher to use, you can encrypt the file using the following commands:

$ openssl enc -aes-256-cbc -salt -in foo.txt -out foo.enc

enter aes-256-cbc encryption password:
Verifying - enter aes-256-cbc encryption password:

$ file foo.enc

foo.enc: data

$ cat foo.enc

Salted__yvi{!e????i"Yt?;(Ѱ e%

$ openssl enc -d -aes-256-cbc -in foo.enc

enter aes-256-cbc decryption password:
test file

In the above example, the file foo.txt was encrypted using 256-bit AES in CBC mode, the encrypted copy being saved as the file foo.enc. Looking at the contents of the file provide gibberish. Decrypting the file is done using the -d option, however keep in mind that not only do you need to remember the password, you also need to know the cipher used.

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