Module crypto 

Content Hash Key (CHK) encryption for HashTree

⚠️ EXPERIMENTAL: Encryption API is unstable and may change.

Uses convergent encryption where the key is derived from the content itself. This enables deduplication: same content → same ciphertext.

Algorithm:

1. content_hash = SHA256(plaintext)
2. key = HKDF-SHA256(content_hash, salt=“hashtree-chk”, info=“encryption-key”)
3. ciphertext = AES-256-GCM(key, zero_nonce, plaintext)

Zero nonce is safe because CHK guarantees same key = same content.

Format: [ciphertext][16-byte auth tag]

The content_hash acts as the “decryption key” - store it securely.

Enums

CryptoError

Encryption error

Functions

content_hash

Compute content hash (SHA256) - this becomes the decryption key for CHK

could_be_encrypted

Check if data could be encrypted (based on minimum size for non-CHK)

decrypt

Decrypt with a provided key (non-CHK)

decrypt_chk

CHK decrypt: derive key from content_hash, decrypt with zero nonce

encrypt

Encrypt with a provided key (non-CHK, random nonce)

encrypt_chk

CHK encrypt: derive key from content, encrypt with zero nonce

encrypted_size

Calculate encrypted size for given plaintext size (non-CHK with nonce prefix)

encrypted_size_chk

Calculate encrypted size for CHK (no nonce prefix)

generate_key

Generate a random 32-byte key (for non-CHK encryption)

key_from_hex

Convert hex string to key

key_to_hex

Convert key to hex string

plaintext_size

Calculate plaintext size from encrypted size (non-CHK)

Type Aliases

EncryptionKey

32-byte encryption key (256 bits) - this is the content hash