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fix: attempt to fix unwrap interop issues #12

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fix: attempt to fix unwrap interop issues #12

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36 changes: 28 additions & 8 deletions didcomm_messaging/crypto/askar/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -190,9 +190,12 @@ async def ecdh_es_encrypt(
enc_key = ecdh.EcdhEs(alg_id, None, None).sender_wrap_key( # type: ignore
wrap_alg, epk, recip_key.key, cek
)
# RFC 3394 key wrapping requires default initial value made up of 8
# bytes of 0xa6 repeated 8 times
aes_wrapped = (b"\xa6" * 8) + enc_key.ciphertext
builder.add_recipient(
JweRecipient(
encrypted_key=enc_key.ciphertext,
encrypted_key=aes_wrapped,
header={"kid": recip_key.kid, "epk": epk.get_jwk_public()},
)
)
Expand All @@ -213,7 +216,7 @@ async def ecdh_es_encrypt(

return builder.build().to_json().encode("utf-8")

async def ecdh_es_decrypt(
async def ecdh_es_decrypt( # noqa: C901
self,
wrapper: Union[JweEnvelope, str, bytes],
recip_key: AskarSecretKey,
Expand Down Expand Up @@ -262,13 +265,21 @@ async def ecdh_es_decrypt(
apv = recip.header.get("apv")
# apu and apv are allowed to be None

# RFC 3394 key wrapping requires default initial value made up of 8
# bytes of 0xa6 repeated 8 times
div = b"\xa6" * 8
if not recip.encrypted_key.startswith(div):
raise CryptoServiceError("Invalid wrapped key")

aes_unwrapped = recip.encrypted_key[len(div) :]

try:
cek = ecdh.EcdhEs(alg_id, apu, apv).receiver_unwrap_key( # type: ignore
wrap_alg,
enc_alg,
epk,
recip_key.key,
recip.encrypted_key,
aes_unwrapped,
)
except AskarError:
raise CryptoServiceError("Error decrypting content encryption key")
Expand Down Expand Up @@ -347,15 +358,16 @@ async def ecdh_1pu_encrypt(
enc_key = ecdh.Ecdh1PU(alg_id, apu, apv).sender_wrap_key(
wrap_alg, epk, sender_key.key, recip_key.key, cek, cc_tag=payload.tag
)
# RFC 3394 key wrapping requires default initial value made up of 8
# bytes of 0xa6 repeated 8 times
aes_wrapped = (b"\xa6" * 8) + enc_key.ciphertext
builder.add_recipient(
JweRecipient(
encrypted_key=enc_key.ciphertext, header={"kid": recip_key.kid}
)
JweRecipient(encrypted_key=aes_wrapped, header={"kid": recip_key.kid})
)

return builder.build().to_json().encode("utf-8")

async def ecdh_1pu_decrypt(
async def ecdh_1pu_decrypt( # noqa: C901
self,
wrapper: Union[JweEnvelope, str, bytes],
recip_key: AskarSecretKey,
Expand Down Expand Up @@ -396,14 +408,22 @@ async def ecdh_1pu_decrypt(
apv = wrapper.protected.get("apv")
# apu and apv are allowed to be None

# RFC 3394 key wrapping requires default initial value made up of 8
# bytes of 0xa6 repeated 8 times
div = b"\xa6" * 8
if not recip.encrypted_key.startswith(div):
raise CryptoServiceError("Invalid wrapped key")

aes_unwrapped = recip.encrypted_key[len(div) :]

try:
cek = ecdh.Ecdh1PU(alg_id, apu, apv).receiver_unwrap_key( # type: ignore
wrap_alg,
enc_alg,
epk,
sender_key.key,
recip_key.key,
recip.encrypted_key,
aes_unwrapped,
cc_tag=wrapper.tag,
)
except AskarError as err:
Expand Down