GOST Kuznyechik cipher
Encrypt or decrypt text with the GOST R 34.12-2015 Kuznyechik 128-bit block cipher — CBC, CTR, CFB, OFB or ECB, 256-bit key, hex or base64. Runs in your browser; nothing is uploaded.
About this tool
GOST Kuznyechik cipher is a low-level encrypt/decrypt tool for the GOST R 34.12-2015 "Kuznyechik" block cipher (also specified in RFC 7801), the modern Russian standard symmetric cipher. You supply the raw key and IV/nonce, pick the mode, and get the result — handy for implementing or testing against the standard, debugging interop, or learning how the cipher works.
- Block / key: Kuznyechik uses a 128-bit (16-byte) block and a fixed 256-bit (32-byte) key.
- Modes:
CBC(default),CTR,CFB,OFB, andECB(insecure, reveals patterns — included for completeness only). CBC and ECB use PKCS7 padding; CTR/CFB/OFB are stream modes (no padding). - Encoding: key, IV and ciphertext are hex or base64; the plaintext is UTF-8 text. CBC/CTR/CFB/OFB need a 16-byte IV; ECB needs none.
Privacy
Everything runs in your browser via WebAssembly — your key and data never leave the device. Also available from the gizza CLI and in chat.
Not sure which tool you want?
If you just want to protect a message with a passphrase (and have the salt,
key derivation and nonce handled safely for you), use the text-encrypt tool
instead — gost-kuznyechik-cipher is for when you already have a specific raw
key, IV and mode.
FAQ
What key and IV sizes does Kuznyechik require here?
The key must be exactly 32 bytes (256 bits) and the IV exactly 16 bytes — both
supplied in the encoding you pick (base64 by default, or hex). CBC, CTR,
CFB and OFB all need the IV; ECB takes none. Anything else is rejected with an
error rather than silently truncated.
Can I type a password instead of a raw key?
No — this is a low-level cipher tool, so the key field expects the raw 256-bit key itself, base64- or hex-encoded, not a passphrase. If you want passphrase-based encryption with salt, key derivation and nonce handled for you, use the text-encrypt tool instead.
Which modes pad the plaintext, and which don't?
CBC and ECB are block modes and apply PKCS7 padding, so the ciphertext is rounded up to a multiple of the 16-byte block. CTR, CFB and OFB are stream modes — no padding, and the ciphertext is exactly as long as the UTF-8 plaintext.
Why is ECB mode listed if it's insecure?
For completeness and interop testing against the GOST R 34.12-2015 / RFC 7801 spec. ECB encrypts each 16-byte block independently, so identical blocks produce identical ciphertext and patterns leak. For anything real, prefer CBC or CTR with a fresh random IV.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool gost-kuznyechik-cipher "Text to encrypt…" 'key=base64 or hex key'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/gost-kuznyechik-cipher/?data=Text%20to%20encrypt%E2%80%A6&operation=encrypt&cipher=cbc&key=base64%20or%20hex%20key&iv=base64%20or%20hex%20iv&format=base64Machine-readable descriptor: tool.json — title + parameters JSON Schema for agents.