Crate ps_cypher 

ps-cypher

Convergent encryption with ChaCha20-Poly1305, zstd, and Reed-Solomon ECC.

Scheme

• The encryption key is the hash of the plaintext (ps-hash): the ChaCha20 key is the hash’s 32-byte digest, and the nonce is derived from the hash’s parity bytes.
• The plaintext is compressed deterministically (zstd level 7 via ps-compress) before encryption.
• The ciphertext is Reed-Solomon encoded (ps-ecc), so up to 12 corrupted bytes per codeword are repaired transparently during decryption.
• Identical inputs therefore always produce identical ciphertexts, keys, and hashes, which enables content-addressed deduplication of encrypted data.
• decrypt re-hashes the decrypted data and fails with KeyMismatch unless it hashes to the decryption key, so a successful decryption returns exactly the data that produced the key.

Example

use ps_cypher::{decrypt, encrypt};

let encrypted = encrypt(b"example payload")?;
let decrypted = decrypt(&encrypted.bytes, &encrypted.key)?;

assert_eq!(&*decrypted, b"example payload");

Security caveats

Convergent encryption is deterministic by design, which leaks information that a randomized cipher would not:

• Plaintext equality: identical plaintexts encrypt to identical ciphertexts, so an observer learns when two stored objects are equal.
• Confirmation and dictionary attacks: anyone who can guess a plaintext can encrypt the guess and compare ciphertexts, confirming whether it is stored. Low-entropy data is therefore not confidential against an adversary who can enumerate candidates.
• Length leakage: the ciphertext length reveals the compressed size of the plaintext, i.e., its length and compressibility.
• validate_ecc is not authentication: it is an unkeyed checksum that detects accidental corruption only, and it returns false for corrupted-but-correctable data that decrypt still accepts. Tampering is detected by the Poly1305 tag during decrypt, and the decrypted data is additionally verified to hash to the decryption key.

Structs

Buffer

Encrypted

ParsedKey

Enums

DecryptionError

Errors returned by decrypt.

EncryptionError

Errors returned by encrypt.

Functions

decrypt

Decrypts data using key, repairing up to 12 corrupted bytes per codeword.

encrypt

Encrypts data using convergent encryption: the key is the hash of data.

extract_encrypted

Extracts the raw ChaCha-encrypted content from the provided slice.

validate_ecc

Checks whether data is a pristine ECC codeword.