A lightweight, zero-dependency, single-file client-side tool for encrypting existing cryptocurrency seed entropy into a secure Base58 text backup. Designed for offline use, it encrypts raw hex entropy (16-byte / 12 words or 32-byte / 24 words) using native WebCrypto API.
- Not Audited: This project is educational and has not undergone a formal security audit.
- Strictly Offline: Run this tool exclusively in an air-gapped browser environment.
- No Seed Generation: This tool does NOT generate new seed phrases; it only encrypts your existing entropy.
SeedCryptor operates directly on raw entropy hex. Converting between mnemonic words and hex is done offline using a trusted tool like iancoleman.io/bip39.
- Extract Hex: Open
iancoleman.io/bip39strictly offline. Enter your mnemonic phrase to view the Entropy hex (32 characters for 12 words / 16B, or 64 characters for 24 words / 32B). - Encrypt: Paste the hex into the corresponding tab in SeedCryptor, enter a password (>= 8 characters), and generate your Base58 backup block.
- Decrypt Hex: Paste your Base58 backup block into SeedCryptor and enter your password to reveal the original 32 or 64-character hex.
- Restore Words: Open
iancoleman.io/bip39offline, navigate to the Entropy section, paste your decrypted hex, and generate your mnemonic words.
| Parameter | Specification |
|---|---|
| KDF | PBKDF2-HMAC-SHA256 (600,000 iterations, 256-bit key) |
| Encryption | AES-GCM 256 |
| Encoding | Base58 (123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz) |
| Dependencies | Pure WebCrypto API + Vanilla JS (Zero external libraries) |
| Network Access | None (Fully air-gapped execution) |
[0 : 16]— Salt (16 bytes)[16 : 28]— Initialization Vector / IV (12 bytes)[28 : end]— Ciphertext + Auth Tag (16 bytes)
- Save
index.htmlto an offline storage device (e.g., USB drive). - Open
index.htmlin any modern web browser on an air-gapped machine. - Select either 16 BYTE (12 words) or 32 BYTE (24 words) tab to begin.