Signal >> Blog >> Advanced cryptographic ratcheting https://signal.org/blog/advanced-ratcheting/
1 of 7 20/03/2019, 08:18
Signal >> Blog >> Advanced cryptographic ratcheting https://signal.org/blog/advanced-ratcheting/
2 of 7 20/03/2019, 08:18
5
6
5
6
5
Signal >> Blog >> Advanced cryptographic ratcheting https://signal.org/blog/advanced-ratcheting/
3 of 7 20/03/2019, 08:18
struct {
opaque sender_key_id[4];
opaque receiver_key_id[4];
opaque next_key_id[4];
opaque next_key[32];
opaque ciphertext[...];
opaque mac[10];
} OTR_Message;
Signal >> Blog >> Advanced cryptographic ratcheting https://signal.org/blog/advanced-ratcheting/
4 of 7 20/03/2019, 08:18
RootKey
RootKey
A1
B1
A1 A2
struct {
opaque sender_ephemeral[32];
opaque body[...]
opaque mac[10]
}
Signal >> Blog >> Advanced cryptographic ratcheting https://signal.org/blog/advanced-ratcheting/
5 of 7 20/03/2019, 08:18
Alice
Sending | Receiving
MK CK RK CK MK
-- -- -- -- --
ECDH(A0,B0)
|
|
ECDH(A1,B0) +
/|
/ |
/ + ECDH(A1,B1)
CK-A1-B0 |\
| | \
MK-0 ----+ | \
| | CK-A1-B1
MK-1 ----+ | |
| | +---- MK-0
MK-2 ----+ | |
| +---- MK-1
ECDH(A2,B1) +
/|
/ |
/ |
CK-A2-B1 |
| + ECDH(A2,B2)
MK-0 ----+ \
\
\
CK-A2-B2
|
+---- MK-0
|
+---- MK-1
RK
RK
struct {
opaque sender_ephemeral_key[32];
opaque counter[3];
opaque mac[10];
}
Signal >> Blog >> Advanced cryptographic ratcheting https://signal.org/blog/advanced-ratcheting/
6 of 7 20/03/2019, 08:18
Signal >> Blog >> Advanced cryptographic ratcheting https://signal.org/blog/advanced-ratcheting/
7 of 7 20/03/2019, 08:18