45 lines
1.4 KiB
Python
45 lines
1.4 KiB
Python
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"""
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AES-256-GCM Cookie encryption / decryption utilities.
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"""
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import base64
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import hashlib
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from Crypto.Cipher import AES
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def derive_key(raw_key: str) -> bytes:
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"""Derive a 32-byte key from an arbitrary string using SHA-256."""
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return hashlib.sha256(raw_key.encode("utf-8")).digest()
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def encrypt_cookie(plaintext: str, key: bytes) -> tuple[str, str]:
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"""
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Encrypt a cookie string with AES-256-GCM.
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Returns:
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(ciphertext_b64, iv_b64) — both base64-encoded strings.
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"""
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cipher = AES.new(key, AES.MODE_GCM)
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ciphertext, tag = cipher.encrypt_and_digest(plaintext.encode("utf-8"))
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# Append the 16-byte tag to the ciphertext so decryption can verify it
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ciphertext_with_tag = ciphertext + tag
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ciphertext_b64 = base64.b64encode(ciphertext_with_tag).decode("utf-8")
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iv_b64 = base64.b64encode(cipher.nonce).decode("utf-8")
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return ciphertext_b64, iv_b64
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def decrypt_cookie(ciphertext_b64: str, iv_b64: str, key: bytes) -> str:
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"""
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Decrypt a cookie string previously encrypted with encrypt_cookie.
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Raises ValueError on decryption failure (wrong key, corrupted data, etc.).
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"""
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raw = base64.b64decode(ciphertext_b64)
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nonce = base64.b64decode(iv_b64)
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# Last 16 bytes are the GCM tag
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ciphertext, tag = raw[:-16], raw[-16:]
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cipher = AES.new(key, AES.MODE_GCM, nonce=nonce)
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plaintext = cipher.decrypt_and_verify(ciphertext, tag)
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return plaintext.decode("utf-8")
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