How to encrypt a file with a password using OpenSSL

Encrypting a file with a password in OpenSSL is useful when one local file must be handed off or stored briefly without setting up public-key recipients. The risky parts are using an old password-derivation path, putting the password on the command line, or sending the encrypted copy before proving it decrypts back to the same bytes.

The openssl enc command wraps file contents with a symmetric cipher and derives the encryption key from a password. Use -pbkdf2 so the password runs through PBKDF2, keep salt enabled, and repeat the same cipher and iteration count during decryption because those choices control how the key is rebuilt.

Treat enc output as password-protected file wrapping, not a complete archival security system. OpenSSL stores a random salt with the encrypted file, but enc does not support authenticated encryption modes such as GCM, so verify the recovered file before trusting it and choose a different file-encryption tool when tamper detection or recipient key management is required.

1. Confirm the file that will be encrypted and choose a separate output filename.

   $ ls -l project-notes.txt
   -rw-r--r-- 1 operator operator 75 Jun  6 10:10 project-notes.txt

   The examples below use project-notes.txt.enc for the encrypted copy and project-notes.decrypted.txt for the recovery test. Keep the original file unchanged until the decrypt-and-hash check passes.

2. Encrypt the file with AES-256-CBC, salt, and PBKDF2 key derivation.

   $ openssl enc -aes-256-cbc -salt -pbkdf2 -iter 200000 -in project-notes.txt -out project-notes.txt.enc
   enter AES-256-CBC encryption password:
   Verifying - enter AES-256-CBC encryption password:

   The password is typed twice and is not echoed back to the terminal. Record the cipher, -pbkdf2, and -iter 200000 with the handoff notes because the decrypt command must use the same values.

   Do not use -pass pass:password for real files. OpenSSL accepts it, but the password can appear in process listings and shell history. For automation, use a protected password file or secret-mounted path with -pass file:/secure/path.

3. Check that the encrypted file was created without replacing the original.

   $ ls -l project-notes.txt project-notes.txt.enc
   -rw-r--r-- 1 operator operator 75 Jun  6 10:10 project-notes.txt
   -rw-r--r-- 1 operator operator 96 Jun  6 10:11 project-notes.txt.enc

   The encrypted file is larger in this small example because OpenSSL stores salt metadata and block padding with the ciphertext.

4. Decrypt the encrypted file to a new filename before sharing or deleting anything.

   $ openssl enc -d -aes-256-cbc -pbkdf2 -iter 200000 -in project-notes.txt.enc -out project-notes.decrypted.txt
   enter AES-256-CBC decryption password:

   Use a different output filename so a failed recovery test cannot overwrite the original file. If the wrong password or wrong iteration count is used, decryption should fail or produce bytes that do not match the original hash.

5. Compare the original and recovered file hashes.

   $ openssl dgst -sha256 project-notes.txt project-notes.decrypted.txt
   SHA2-256(project-notes.txt)= 70113d26a9f27637aef811364573e856b047494d0671bae701e7206cfe812e84
   SHA2-256(project-notes.decrypted.txt)= 70113d26a9f27637aef811364573e856b047494d0671bae701e7206cfe812e84

   Matching SHA-256 values prove that the decrypted file has the same bytes as the source file used for the test. Send the password through a separate channel from the encrypted file.