SPECK Encryption

Speck encryption online

Speck is a family of lightweight ARX block ciphers designed for efficient software implementation. The SIMON and SPECK specification defines ten variants, named by block size and key size; for example, Speck64/128 has a 64-bit block and a 128-bit key. This tool supports all ten published variants.

How to use this tool

Select the exact Speck variant used by the other implementation. Enter plaintext using the chosen input encoding and supply a key of the required byte length. The plaintext length must be an exact multiple of the selected variant’s block size. Encrypt it and copy the Hex or Base64 ciphertext.

Matching cipher parameters

This page applies the raw Speck block transformation independently to each complete block. It does not add a block mode, padding, IV, salt, or passphrase derivation. The variant, key bytes, block order, and encodings must match the receiving implementation or Speck decryption.

Hex and Base64 only represent the ciphertext bytes. If the input is not already block-aligned, define padding or a higher-level format outside this tool and remove it consistently after decryption.

Security warning

Raw block encryption is deterministic: equal plaintext blocks under the same key produce equal ciphertext blocks and expose patterns. It also provides no integrity or authentication. Use Speck here for test vectors and explicit legacy interoperability, not as a complete encryption format for new applications; prefer a reviewed authenticated encryption scheme such as AES encryption.

Frequently asked questions

Why can I not decrypt the result elsewhere?

Compare the exact variant, key bytes, byte order, plaintext encoding, and ciphertext encoding. This page does not use a mode, padding, IV, passphrase, or salt.

Does encryption detect tampering?

No. The raw Speck transformation has no authentication tag and cannot show whether ciphertext was changed.