28 lines
952 B
Python
28 lines
952 B
Python
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"""AES-256-GCM helpers matching static/js/app.js's encryptBytes/decryptBytes
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(Web Crypto AES-GCM, 12-byte IV hex-encoded, ciphertext base64, key handled
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as raw bytes) — diora's books are end-to-end encrypted client-side, so the
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server (and this module) only ever sees ciphertext plus the key the user
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supplies out-of-band.
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"""
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from __future__ import annotations
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import base64
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from cryptography.exceptions import InvalidTag
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from cryptography.hazmat.primitives.ciphers.aead import AESGCM
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class DecryptError(Exception):
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"""Ciphertext could not be decrypted with the given key (wrong key, or corrupt data)."""
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def decrypt(key_b64: str, iv_hex: str, ciphertext_b64: str) -> bytes:
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try:
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key = base64.b64decode(key_b64)
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iv = bytes.fromhex(iv_hex)
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ct = base64.b64decode(ciphertext_b64)
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return AESGCM(key).decrypt(iv, ct, None)
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except (InvalidTag, ValueError) as e:
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raise DecryptError(str(e)) from e
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