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How to Decrypt Text with OpenSSL

Decrypt OpenSSL enc output by matching its cipher, PBKDF2, digest, salt, and Base64 settings, then verify the recovered bytes.

Encrypt Online Editorial Team5 min read
How to Decrypt Text with OpenSSL guide cover

Before you start

Run the workflow once with a disposable value, then do a decrypt or restore check before you share anything real.

An OpenSSL passphrase is only one part of a successful decrypt. The cipher, password derivation, digest, iteration count, salt handling, and Base64 settings must agree with the original encryption command.

If the command was not recorded, a correct passphrase may still be insufficient.

In brief

Reconstruct the original openssl enc recipe before changing flags at random. Match the cipher and PBKDF2 settings first, then confirm whether the encrypted input is raw binary or Base64 text.

After decryption, compare the recovered bytes with a known value. No error message does not automatically mean the plaintext is authentic or correct.

Collect evidence before retrying

Write down what is known:

  • The exact cipher and mode, such as aes-256-cbc.
  • Whether encryption used a passphrase or a raw key and IV.
  • Whether -pbkdf2 or -iter was present, plus the iteration count.
  • The digest supplied with -md.
  • Whether the encrypted value was Base64 encoded with -a, and whether it was written as one line with -A.
  • Whether the salt was generated normally, disabled with -nosalt, or supplied explicitly with -S.
  • Whether OpenSSL 3.2 or later used a non-default -saltlen value with PBKDF2.
  • The OpenSSL version used to create the data.

Randomly generated salt is normally stored after the Salted__ marker at the beginning of the encrypted data. The envelope does not separately identify the salt length, cipher, or KDF settings, so preserve the original command whenever possible.

Run the matching decrypt command

For output created with the companion recipe in this guide set, use:

Shell
openssl enc -d -aes-256-cbc -pbkdf2 -iter 100000 -md sha256 \
  -a -A -in message.enc -out message.txt

Remove -A when the Base64 input has normal line wrapping. Remove both -a and -A when the encrypted input is binary. Change the cipher, iteration count, and digest only to match the original encryption settings.

If the recipe is uncertain, start with the OpenSSL AES Decrypt Checker. It can inspect the envelope, test supported settings in your browser, and build a command without placing the passphrase in it.

Work through bad decrypt in order

bad decrypt means the final decrypt or padding check failed. It does not identify which input was wrong. Check one layer at a time:

  1. Confirm whether the input is binary or Base64. For one-line Base64, match -a -A; for wrapped Base64, use -a.
  2. Match the cipher and mode, such as aes-256-cbc.
  3. Match the KDF. Do not add -pbkdf2 when the original command did not use it.
  4. Match the PBKDF2 iteration count and -md digest. OpenSSL changed its default digest from MD5 to SHA-256 in version 1.1.0.
  5. Match generated, explicit, or disabled salt handling, plus -saltlen when OpenSSL 3.2 or later used it.
  6. Recheck the passphrase and look for copied, truncated, or damaged input.

CBC padding is only a weak check. Incorrect settings can occasionally produce output without a hard error, so readable output is not proof of integrity.

Match salt rules by OpenSSL version

Avoid adding -S unless the encryption recipe used an explicit salt. If it did, supply the same hexadecimal salt during decryption.

OpenSSL 3.0 changed this behavior: an explicit -S value is no longer prepended during encryption. Data created with an explicit salt under OpenSSL 1.1.1 may therefore need a different decrypt command than data created under OpenSSL 3.0 or later. Check openssl version before copying an old recipe unchanged.

OpenSSL 3.2 added -saltlen for PBKDF2. The default remains eight bytes and the current maximum is 16; encryption and decryption must use the same length. Earlier versions use the fixed eight-byte salt behavior.

Verify the recovered bytes

A round-trip comparison is the cleanest check when you still have the original:

Shell
cmp -s message.original message.txt && echo 'exact match'
openssl dgst -sha256 message.txt

When the original is unavailable, compare against a checksum from a trusted source or a precise expected structure. A familiar-looking first line is a useful clue, not proof that every byte is correct.

Keep browser decrypt formats separate

The Encrypt Online homepage and /decrypt do not implement the PBKDF2 openssl enc recipe in this article. Pasting this ciphertext there will not reproduce the command-line result. Use OpenSSL with the original parameters or the dedicated OpenSSL AES Decrypt Checker.

The Base64 Decode tool can help identify wrapping or copy damage, but it only decodes the transport text. It does not decrypt OpenSSL ciphertext.

Questions behind common failures

What if I know only the password?

Try to recover the original command, application documentation, or sender's settings. OpenSSL cannot reliably infer the cipher and password-derivation choices from a normal enc payload.

Should I add -pbkdf2 when an old command did not use it?

No. PBKDF2 is the better choice when creating a new password-based recipe, but decryption must reproduce the method used to create the existing ciphertext. Adding it changes the derived key and IV.

Why did -a work but -a -A was needed after copying the value?

Normal Base64 output contains line breaks. A chat field, environment variable, or clipboard step may collapse it to one line. -A changes OpenSSL's Base64 handling so it does not require those newlines.

References

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