SPECK Decryption
This online tool helps you decrypt strings using the SPECK block cipher. It uses raw complete blocks without mode or padding. Expand to read more.
Speck decryption online
Speck decryption reverses the lightweight ARX block cipher with the same variant and key used for encryption. The original SIMON and SPECK specification defines ten combinations of block and key size, from Speck32/64 through Speck128/256. This tool supports each published combination.
How to use this tool
Choose the ciphertext encoding and exact Speck variant, then enter a key of the required byte length. The decoded ciphertext must be a multiple of that variant’s block size. Decrypt it and select the output encoding needed to display the recovered bytes.
Matching cipher parameters
This page reverses raw, complete Speck blocks such as those produced by Speck encryption. It has no mode, padding, IV, salt, or KDF. Formats that wrap Speck in a mode or padding scheme require those layers to be handled separately.
Security warning
Wrong key bytes or a wrong variant normally produce unrelated output without a dependable error because raw Speck has no authentication tag. Use this page for test vectors and explicit legacy interoperability. For a modern authenticated format, use the matching implementation’s authenticated decryption or AES decryption.
Frequently asked questions
Why can I not recover the original plaintext?
Compare the full variant name, key bytes, byte order, ciphertext encoding, and expected plaintext encoding. If the source added padding or used a block mode, this raw-block page is not directly compatible with that ciphertext.
Does encryption detect tampering?
No. Readable output does not prove the ciphertext is authentic or unchanged. Integrity must be supplied by the surrounding format or protocol.