|
|
|
@ -17,12 +17,12 @@ side of an \(=\) it means that the output is split.
|
|
|
|
When this document uses \(\operatorname{ECDH}\left(K_A,K_B\right)\) it means
|
|
|
|
When this document uses \(\operatorname{ECDH}\left(K_A,K_B\right)\) it means
|
|
|
|
that each party computes a Diffie-Hellman agreement using their private key
|
|
|
|
that each party computes a Diffie-Hellman agreement using their private key
|
|
|
|
and the remote party's public key.
|
|
|
|
and the remote party's public key.
|
|
|
|
So party \(A\) computes \(\operatorname{ECDH}\left(K_B^{\mathit{public}},K_A^{\mathit{private}}\right)\)
|
|
|
|
So party \(A\) computes \(\operatorname{ECDH}\left(K_B^{public},K_A^{private}\right)\)
|
|
|
|
and party \(B\) computes \(\operatorname{ECDH}\left(K_A^{\mathit{public}},K_B^{\mathit{private}}\right)\).
|
|
|
|
and party \(B\) computes \(\operatorname{ECDH}\left(K_A^{public},K_B^{private}\right)\).
|
|
|
|
|
|
|
|
|
|
|
|
Where this document uses \(\operatorname{HKDF}\left(\mathit{salt},\mathit{IKM},\mathit{info},L\right)\) it
|
|
|
|
Where this document uses \(\operatorname{HKDF}\left(salt,IKM,info,L\right)\) it
|
|
|
|
refers to the [HMAC-based key derivation function][] with a salt value of
|
|
|
|
refers to the [HMAC-based key derivation function][] with a salt value of
|
|
|
|
\(\mathit{salt}\), input key material of \(\mathit{IKM}\), context string \(\mathit{info}\),
|
|
|
|
\(salt\), input key material of \(IKM\), context string \(info\),
|
|
|
|
and output keying material length of \(L\) bytes.
|
|
|
|
and output keying material length of \(L\) bytes.
|
|
|
|
|
|
|
|
|
|
|
|
## The Olm Algorithm
|
|
|
|
## The Olm Algorithm
|
|
|
|
@ -226,9 +226,9 @@ significant bits are stored in the first byte.
|
|
|
|
|
|
|
|
|
|
|
|
**Name**|**Tag**|**Type**|**Meaning**
|
|
|
|
**Name**|**Tag**|**Type**|**Meaning**
|
|
|
|
:-----:|:-----:|:-----:|:-----:
|
|
|
|
:-----:|:-----:|:-----:|:-----:
|
|
|
|
Ratchet-Key|0x0A|String|The public part of the ratchet key of the message, \(T_i\).
|
|
|
|
Ratchet-Key|0x0A|String|The public part of the ratchet key, Ti, of the message
|
|
|
|
Chain-Index|0x10|Integer|The chain index of the message, \(j\).
|
|
|
|
Chain-Index|0x10|Integer|The chain index, j, of the message
|
|
|
|
Cipher-Text|0x22|String|The cipher-text of the message, \(X_{i,j}\).
|
|
|
|
Cipher-Text|0x22|String|The cipher-text, Xi, j, of the message
|
|
|
|
|
|
|
|
|
|
|
|
The length of the MAC is determined by the authenticated encryption algorithm
|
|
|
|
The length of the MAC is determined by the authenticated encryption algorithm
|
|
|
|
being used. (Olm version 1 uses [HMAC-SHA-256][], truncated to 8 bytes). The
|
|
|
|
being used. (Olm version 1 uses [HMAC-SHA-256][], truncated to 8 bytes). The
|
|
|
|
@ -251,9 +251,9 @@ The payload uses the same key-value format as for normal messages.
|
|
|
|
|
|
|
|
|
|
|
|
**Name**|**Tag**|**Type**|**Meaning**
|
|
|
|
**Name**|**Tag**|**Type**|**Meaning**
|
|
|
|
:-----:|:-----:|:-----:|:-----:
|
|
|
|
:-----:|:-----:|:-----:|:-----:
|
|
|
|
One-Time-Key|0x0A|String|The public part of Bob's single-use key, \(E_B\).
|
|
|
|
One-Time-Key|0x0A|String|The public part of Bob's single-use key, Eb.
|
|
|
|
Base-Key|0x12|String|The public part of Alice's single-use key, \(E_A\).
|
|
|
|
Base-Key|0x12|String|The public part of Alice's single-use key, Ea.
|
|
|
|
Identity-Key|0x1A|String|The public part of Alice's identity key, \(I_A\).
|
|
|
|
Identity-Key|0x1A|String|The public part of Alice's identity key, Ia.
|
|
|
|
Message|0x22|String|An embedded Olm message with its own version and MAC.
|
|
|
|
Message|0x22|String|An embedded Olm message with its own version and MAC.
|
|
|
|
|
|
|
|
|
|
|
|
## Olm Authenticated Encryption
|
|
|
|
## Olm Authenticated Encryption
|
|
|
|
@ -268,13 +268,13 @@ message key using [HKDF-SHA-256][] using the default salt and an info of
|
|
|
|
|
|
|
|
|
|
|
|
\[
|
|
|
|
\[
|
|
|
|
\begin{aligned}
|
|
|
|
\begin{aligned}
|
|
|
|
\mathit{AES\_KEY}_{i,j}\;\parallel\;\mathit{HMAC\_KEY}_{i,j}\;\parallel\;\mathit{AES\_IV}_{i,j}
|
|
|
|
AES\_KEY_{i,j}\;\parallel\;HMAC\_KEY_{i,j}\;\parallel\;AES\_IV_{i,j}
|
|
|
|
&= \operatorname{HKDF}\left(0,M_{i,j},\text{``OLM\_KEYS"},80\right)
|
|
|
|
&= \operatorname{HKDF}\left(0,M_{i,j},\text{``OLM\_KEYS"},80\right)
|
|
|
|
\end{aligned}
|
|
|
|
\end{aligned}
|
|
|
|
\]
|
|
|
|
\]
|
|
|
|
|
|
|
|
|
|
|
|
The plain-text is encrypted with AES-256, using the key \(\mathit{AES\_KEY}_{i,j}\)
|
|
|
|
The plain-text is encrypted with AES-256, using the key \(AES\_KEY_{i,j}\)
|
|
|
|
and the IV \(\mathit{AES\_IV}_{i,j}\) to give the cipher-text, \(X_{i,j}\).
|
|
|
|
and the IV \(AES\_IV_{i,j}\) to give the cipher-text, \(X_{i,j}\).
|
|
|
|
|
|
|
|
|
|
|
|
Then the entire message (including the Version Byte and all Payload Bytes) are
|
|
|
|
Then the entire message (including the Version Byte and all Payload Bytes) are
|
|
|
|
passed through [HMAC-SHA-256][]. The first 8 bytes of the MAC are appended to the message.
|
|
|
|
passed through [HMAC-SHA-256][]. The first 8 bytes of the MAC are appended to the message.
|
|
|
|
|