56 lines
2.5 KiB
Python
56 lines
2.5 KiB
Python
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# cryptomator-utils: Python utilities for inspecting Cryptomator drives
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# Copyright (C) 2024 Lee Yingtong Li (RunasSudo)
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Affero General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <https://www.gnu.org/licenses/>.
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from Crypto.Cipher import AES
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from cryptography.hazmat.primitives.ciphers.aead import AESSIV
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def aes_siv_encrypt(primary_master_key, hmac_master_key, plaintext, associated_data):
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"""
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Encrypt the given bytes using AES-SIV
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"""
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if len(plaintext) == 0:
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# Must use PyCryptodome
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# https://github.com/pyca/cryptography/issues/10958 - cryptography AESSIV does not accept empty plaintext (e.g. root directory has empty directory ID)
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if associated_data:
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if len(associated_data) > 1:
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# Incompatible with PyCryptodome
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raise ValueError('Cannot encrypt zero-length plaintext with AES-SIV with >1 associated data')
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if not associated_data[0]:
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# Incompatible with PyCryptodome
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raise ValueError('Cannot encrypt zero-length plaintext with AES-SIV with zero-length associated data')
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# If there is only one associated data, this is equivalent to the nonce, so we can use PyCryptodome
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ciphertext, tag = AES.new(hmac_master_key + primary_master_key, AES.MODE_SIV, nonce=associated_data[0]).encrypt_and_digest(plaintext)
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return tag + ciphertext
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# Zero-length plaintext with no AAD - encrypt with PyCryptodome
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ciphertext, tag = AES.new(hmac_master_key + primary_master_key, AES.MODE_SIV).encrypt_and_digest(plaintext)
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return tag + ciphertext
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# In all other cases, use cryptography AESSIV
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tag_and_ciphertext = AESSIV(hmac_master_key + primary_master_key).encrypt(plaintext, associated_data)
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return tag_and_ciphertext
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def aes_siv_decrypt(primary_master_key, hmac_master_key, tag_and_ciphertext, associated_data):
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"""
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Decrypt the given AES-SIV ciphertext
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"""
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# Use cryptography AESSIV
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return AESSIV(hmac_master_key + primary_master_key).decrypt(tag_and_ciphertext, associated_data)
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