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Casascius Mini Key

Validate a Casascius mini private key by its SHA-256 typo checksum and derive the Bitcoin private key, WIF and address it protects — entirely in your browser.

minikey
Enter a 22- or 30-character Casascius mini key. Validity = SHA256(key + "?") starts with 0x00; private key = SHA256(key). Replace unknown characters with "?" to brute-force them.
Instructions:
1. Enter a Casascius mini private key (22 or 30 characters, starting with S).
2. Validity is checked with the built-in typo checksum: SHA256(key + "?") must start with 0x00.
3. The private key is derived as d = SHA256(key); the funded address uses the uncompressed public key.
4. Replace any unknown character with "?" to brute-force it (keep to 3 or fewer unknowns).
Educational tool — runs 100% in your browser. A Casascius "mini private key" is a short, typo-checked encoding of a Bitcoin private key (used on physical Casascius coins & bars). This tool validates the checksum, derives the key with d = SHA256(minikey), and shows the uncompressed address that classic coins funded. Never enter a mini key for a wallet you still use.