diff options
Diffstat (limited to 'filecrypt.py')
| -rw-r--r-- | filecrypt.py | 45 |
1 files changed, 25 insertions, 20 deletions
diff --git a/filecrypt.py b/filecrypt.py index ce6e3a1..85d9eea 100644 --- a/filecrypt.py +++ b/filecrypt.py @@ -8,6 +8,7 @@ import os FILE_ID_LENGTH = 22 TOKEN_LENGTH = 22 +HEADER_LENGTH = 56 def encrypt_file(filename_in, chunk_size=1000000//16): file_id = secrets.token_urlsafe(16) @@ -24,6 +25,7 @@ def encrypt_file(filename_in, chunk_size=1000000//16): fout.write(token_tag) # 16 bytes fout.write(auth_secret) # 16 bytes fout.write(data_nonce) # 8 bytes + assert fout.tell() == HEADER_LENGTH cipher = AES.new(key, AES.MODE_CTR, initial_value=struct.pack('<Q', 0), nonce=data_nonce) @@ -37,7 +39,7 @@ def encrypt_file(filename_in, chunk_size=1000000//16): return file_id, token def payload_size(path): - return os.stat(path).st_size - 56 + return os.stat(path).st_size - HEADER_LENGTH def decrypt_generator(filename, token, seek=0, end=None, chunk_size=1000000//16): with open(filename, 'rb') as fin: @@ -45,27 +47,30 @@ def decrypt_generator(filename, token, seek=0, end=None, chunk_size=1000000//16) token_tag = fin.read(16) auth_secret = fin.read(16) data_nonce = fin.read(8) + assert fin.tell() == HEADER_LENGTH - ciphertext = base64.b64decode(token + '='*((3-len(token)%3)%3)) - token_cipher = AES.new(auth_secret, AES.MODE_GCM, nonce=token_nonce) - key = token_cipher.decrypt_and_verify(ciphertext, token_tag) + ciphertext = base64.b64decode(token + '='*((3-len(token)%3)%3)) + token_cipher = AES.new(auth_secret, AES.MODE_GCM, nonce=token_nonce) + key = token_cipher.decrypt_and_verify(ciphertext, token_tag) - # Use token cipher's block size assuming the two are the same - cipher = AES.new(key, AES.MODE_CTR, - initial_value=struct.pack('>Q', seek // token_cipher.block_size), nonce=data_nonce) - print('Seeking to position', seek, 'iv', seek // token_cipher.block_size, 'pos', seek - seek % - cipher.block_size, 'offset', seek % cipher.block_size) - fin.seek(seek - seek % cipher.block_size, 1) - offset = seek % cipher.block_size + def generator(): + with open(filename, 'rb') as fin: + fin.seek(HEADER_LENGTH) + # Use token cipher's block size assuming the two are the same + cipher = AES.new(key, AES.MODE_CTR, + initial_value=struct.pack('>Q', seek // token_cipher.block_size), nonce=data_nonce) + fin.seek(seek - seek % cipher.block_size, 1) + offset = seek % cipher.block_size - to_send = end - seek + 1 if end else None - block = fin.read(cipher.block_size*chunk_size) - while block and (to_send is None or to_send > 0): - data = cipher.decrypt(block) - out = data[offset:to_send] - yield out - if to_send is not None: - to_send -= len(out) - offset = 0 + to_send = end - seek + 1 if end else None block = fin.read(cipher.block_size*chunk_size) + while block and (to_send is None or to_send > 0): + data = cipher.decrypt(block) + out = data[offset:to_send] + yield out + if to_send is not None: + to_send -= len(out) + offset = 0 + block = fin.read(cipher.block_size*chunk_size) + return generator() |