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-rw-r--r--src/leap/soledad/backends/leap_backend.py83
1 files changed, 79 insertions, 4 deletions
diff --git a/src/leap/soledad/backends/leap_backend.py b/src/leap/soledad/backends/leap_backend.py
index 6f1f9546..87f63432 100644
--- a/src/leap/soledad/backends/leap_backend.py
+++ b/src/leap/soledad/backends/leap_backend.py
@@ -25,6 +25,8 @@ try:
import simplejson as json
except ImportError:
import json # noqa
+import hashlib
+import hmac
from u1db import Document
@@ -37,6 +39,7 @@ from leap.common.keymanager import KeyManager
from leap.common.check import leap_assert
from leap.soledad.auth import TokenBasedAuth
+
#
# Exceptions
#
@@ -52,6 +55,21 @@ class UnknownEncryptionScheme(Exception):
"""
Raised when trying to decrypt from unknown encryption schemes.
"""
+ pass
+
+
+class UnknownMacMethod(Exception):
+ """
+ Raised when trying to authenticate document's content with unknown MAC
+ mehtod.
+ """
+ pass
+
+
+class WrongMac(Exception):
+ """
+ Raised when failing to authenticate document's contents based on MAC.
+ """
#
@@ -68,12 +86,55 @@ class EncryptionSchemes(object):
PUBKEY = 'pubkey'
+class MacMethods(object):
+ """
+ Representation of MAC methods used to authenticate document's contents.
+ """
+
+ HMAC = 'hmac'
+
+
#
# Crypto utilities for a LeapDocument.
#
ENC_JSON_KEY = '_enc_json'
ENC_SCHEME_KEY = '_enc_scheme'
+MAC_KEY = '_mac'
+MAC_METHOD_KEY = '_mac_method'
+
+
+def mac_doc(crypto, doc_id, doc_rev, ciphertext, mac_method):
+ """
+ Calculate a MAC for C{doc} using C{ciphertext}.
+
+ Current MAC method used is HMAC, with the following parameters:
+
+ * key: sha256(storage_secret, doc_id)
+ * msg: doc_id + doc_rev + ciphertext
+ * digestmod: sha256
+
+ @param crypto: A SoledadCryto instance used to perform the encryption.
+ @type crypto: leap.soledad.crypto.SoledadCrypto
+ @param doc_id: The id of the document.
+ @type doc_id: str
+ @param doc_rev: The revision of the document.
+ @type doc_rev: str
+ @param ciphertext: The content of the document.
+ @type ciphertext: str
+ @param mac_method: The MAC method to use.
+ @type mac_method: str
+
+ @return: The calculated MAC.
+ @rtype: str
+ """
+ if mac_method == MacMethods.HMAC:
+ return hmac.new(
+ crypto.doc_mac_key(doc_id),
+ str(doc_id) + str(doc_rev) + ciphertext,
+ hashlib.sha256).hexdigest()
+ # raise if we do not know how to handle this MAC method
+ raise UnknownMacMethod('Unknown MAC method: %s.' % mac_method)
def encrypt_doc(crypto, doc):
@@ -85,6 +146,8 @@ def encrypt_doc(crypto, doc):
{
ENC_JSON_KEY: '<encrypted doc JSON string>',
ENC_SCHEME_KEY: 'symkey',
+ MAC_KEY: '<mac>'
+ MAC_METHOD_KEY: 'hmac'
}
@param crypto: A SoledadCryto instance used to perform the encryption.
@@ -100,16 +163,17 @@ def encrypt_doc(crypto, doc):
# encrypt content
ciphertext = crypto.encrypt_sym(
doc.get_json(),
- crypto.passphrase_hash(doc.doc_id))
+ crypto.doc_passphrase(doc.doc_id))
# verify it is indeed encrypted
if not crypto.is_encrypted_sym(ciphertext):
raise DocumentNotEncrypted('Failed encrypting document.')
- # calculate hmac
- #mac = hmac.new(doc_id,, doc_json,
# update doc's content with encrypted version
return json.dumps({
ENC_JSON_KEY: ciphertext,
ENC_SCHEME_KEY: EncryptionSchemes.SYMKEY,
+ MAC_KEY: mac_doc(
+ crypto, doc.doc_id, doc.rev, ciphertext, MacMethods.HMAC),
+ MAC_METHOD_KEY: MacMethods.HMAC,
})
@@ -124,6 +188,8 @@ def decrypt_doc(crypto, doc):
{
ENC_JSON_KEY: '<enc_blob>',
ENC_SCHEME_KEY: '<enc_scheme>',
+ MAC_KEY: '<mac>'
+ MAC_METHOD_KEY: 'hmac'
}
C{enc_blob} is the encryption of the JSON serialization of the document's
@@ -141,6 +207,15 @@ def decrypt_doc(crypto, doc):
leap_assert(doc.is_tombstone() is False)
leap_assert(ENC_JSON_KEY in doc.content)
leap_assert(ENC_SCHEME_KEY in doc.content)
+ leap_assert(MAC_KEY in doc.content)
+ leap_assert(MAC_METHOD_KEY in doc.content)
+ # verify MAC
+ mac = mac_doc(
+ crypto, doc.doc_id, doc.rev,
+ doc.content[ENC_JSON_KEY],
+ doc.content[MAC_METHOD_KEY])
+ if doc.content[MAC_KEY] != mac:
+ raise WrongMac('Could not authenticate document\'s contents.')
# decrypt doc's content
ciphertext = doc.content[ENC_JSON_KEY]
enc_scheme = doc.content[ENC_SCHEME_KEY]
@@ -153,7 +228,7 @@ def decrypt_doc(crypto, doc):
'symmetric key.')
plainjson = crypto.decrypt_sym(
ciphertext,
- crypto.passphrase_hash(doc.doc_id))
+ crypto.doc_passphrase(doc.doc_id))
else:
raise UnknownEncryptionScheme(enc_scheme)
return plainjson