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authorTomás Touceda <chiiph@leap.se>2013-05-15 20:25:00 -0300
committerTomás Touceda <chiiph@leap.se>2013-05-15 20:25:00 -0300
commitf216391f92ac0a52e11e9b13c149c8d40b446aeb (patch)
tree42d99a0a8e35d38bb168320b8a9841e290f978f8 /src/leap/soledad/backends/leap_backend.py
parent021078750d24162d24d7474f8b1fe97ef9467784 (diff)
parent7e6f458af4c7b51f414d6303942fec10dd56d2d3 (diff)
Merge remote-tracking branch 'drebs/feature/2349-add-mac-auth-3' into develop
Diffstat (limited to 'src/leap/soledad/backends/leap_backend.py')
-rw-r--r--src/leap/soledad/backends/leap_backend.py158
1 files changed, 114 insertions, 44 deletions
diff --git a/src/leap/soledad/backends/leap_backend.py b/src/leap/soledad/backends/leap_backend.py
index 2585379a..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
#
@@ -48,10 +51,25 @@ class DocumentNotEncrypted(Exception):
pass
-class UnknownEncryptionSchemes(Exception):
+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.
+ """
#
@@ -68,6 +86,14 @@ 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.
#
@@ -75,53 +101,95 @@ class EncryptionSchemes(object):
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:
-def encrypt_doc_json(crypto, doc_id, doc_json):
+ * 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
"""
- Return a valid JSON string containing the C{doc} content encrypted to
- a symmetric key and the encryption scheme.
+ 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)
- The returned JSON string is the serialization of the following dictionary:
+
+def encrypt_doc(crypto, doc):
+ """
+ Encrypt C{doc}'s content.
+
+ Return a valid JSON string representing the following:
{
- '_enc_json': encrypt_sym(doc_content),
- '_enc_scheme': 'symkey',
- '_mac': <mac> [Not implemented yet]
+ ENC_JSON_KEY: '<encrypted doc JSON string>',
+ ENC_SCHEME_KEY: 'symkey',
+ MAC_KEY: '<mac>'
+ MAC_METHOD_KEY: 'hmac'
}
- @param crypto: A SoledadCryto instance to perform the encryption.
+ @param crypto: A SoledadCryto instance used to perform the encryption.
@type crypto: leap.soledad.crypto.SoledadCrypto
- @param doc_id: The unique id of the document.
- @type doc_id: str
- @param doc_json: The JSON serialization of the document's contents.
- @type doc_json: str
+ @param doc: The document with contents to be encrypted.
+ @type doc: LeapDocument
- @return: The JSON serialization representing the encrypted content.
+ @return: The JSON serialization of the dict representing the encrypted
+ content.
@rtype: str
"""
+ leap_assert(doc.is_tombstone() is False)
+ # encrypt content
ciphertext = crypto.encrypt_sym(
- doc_json,
- crypto.passphrase_hash(doc_id))
+ doc.get_json(),
+ crypto.doc_passphrase(doc.doc_id))
+ # verify it is indeed encrypted
if not crypto.is_encrypted_sym(ciphertext):
raise DocumentNotEncrypted('Failed encrypting document.')
+ # 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,
})
-def decrypt_doc_json(crypto, doc_id, doc_json):
+def decrypt_doc(crypto, doc):
"""
- Return a JSON serialization of the decrypted content contained in
- C{encrypted_json}.
+ Decrypt C{doc}'s content.
+
+ Return the JSON string representation of the document's decrypted content.
- The C{encrypted_json} parameter is the JSON serialization of the
- following dictionary:
+ The content of the document should have the following structure:
{
- ENC_JSON_KEY: enc_blob,
- ENC_SCHEME_KEY: enc_scheme,
+ 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
@@ -130,22 +198,27 @@ def decrypt_doc_json(crypto, doc_id, doc_json):
@param crypto: A SoledadCryto instance to perform the encryption.
@type crypto: leap.soledad.crypto.SoledadCrypto
- @param doc_id: The unique id of the document.
- @type doc_id: str
- @param doc_json: The JSON serialization representation of the encrypted
- document's contents.
- @type doc_json: str
+ @param doc: The document to be decrypted.
+ @type doc: LeapDocument
@return: The JSON serialization of the decrypted content.
@rtype: str
"""
- leap_assert(isinstance(doc_id, str), 'Document id is not a string.')
- leap_assert(doc_id != '', 'Received empty document id.')
- leap_assert(isinstance(doc_json, str), 'Document JSON is not a string.')
- leap_assert(doc_json != '', 'Received empty document JSON.')
- content = json.loads(doc_json)
- ciphertext = content[ENC_JSON_KEY]
- enc_scheme = content[ENC_SCHEME_KEY]
+ 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]
plainjson = None
if enc_scheme == EncryptionSchemes.SYMKEY:
if not crypto.is_encrypted_sym(ciphertext):
@@ -155,9 +228,9 @@ def decrypt_doc_json(crypto, doc_id, doc_json):
'symmetric key.')
plainjson = crypto.decrypt_sym(
ciphertext,
- crypto.passphrase_hash(doc_id))
+ crypto.doc_passphrase(doc.doc_id))
else:
- raise UnknownEncryptionSchemes(enc_scheme)
+ raise UnknownEncryptionScheme(enc_scheme)
return plainjson
@@ -354,9 +427,7 @@ class LeapSyncTarget(HTTPSyncTarget, TokenBasedAuth):
if doc.content and ENC_SCHEME_KEY in doc.content:
if doc.content[ENC_SCHEME_KEY] == \
EncryptionSchemes.SYMKEY:
- doc.set_json(
- decrypt_doc_json(
- self._crypto, doc.doc_id, entry['content']))
+ doc.set_json(decrypt_doc(self._crypto, doc))
#-------------------------------------------------------------
# end of symmetric decryption
#-------------------------------------------------------------
@@ -433,15 +504,14 @@ class LeapSyncTarget(HTTPSyncTarget, TokenBasedAuth):
#-------------------------------------------------------------
# symmetric encryption of document's contents
#-------------------------------------------------------------
- enc_json = doc.get_json()
+ doc_json = doc.get_json()
if not doc.is_tombstone():
- enc_json = encrypt_doc_json(
- self._crypto, doc.doc_id, doc.get_json())
+ doc_json = encrypt_doc(self._crypto, doc)
#-------------------------------------------------------------
# end of symmetric encryption
#-------------------------------------------------------------
size += prepare(id=doc.doc_id, rev=doc.rev,
- content=enc_json,
+ content=doc_json,
gen=gen, trans_id=trans_id)
entries.append('\r\n]')
size += len(entries[-1])