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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/megolm.md | 33 |
1 files changed, 17 insertions, 16 deletions
diff --git a/docs/megolm.md b/docs/megolm.md index 1cfd105..58ea10b 100644 --- a/docs/megolm.md +++ b/docs/megolm.md @@ -271,12 +271,13 @@ future research. (also called 'future secrecy' or 'post-compromise security') is the property that if current private keys are compromised, an attacker cannot decrypt future messages in a given session. In other words, when looking -**backwards** into the past at a compromise, messages sent since the compromise -will be secret. +**backwards** in time at a compromise which has already happened, **current** +messages are still secret. -By itself, Megolm does not posess this property: once the key to a Megolm -session is compromised, the attacker can decrypt any future messages sent via -that session. +By itself, Megolm does not possess this property: once the key to a Megolm +session is compromised, the attacker can decrypt any message that was +encrypted using a key derived from the compromised key or any following +ratchet values. In order to mitigate this, the application should ensure that Megolm sessions are not used indefinitely. Instead it should periodically start a new session, @@ -288,17 +289,17 @@ with new keys shared over a secure channel. ### Partial Forward Secrecy [Forward secrecy](https://intensecrypto.org/public/lec_08_hash_functions_part2.html#sec-forward-and-backward-secrecy) -is the property that if the current private keys are compromised, an attacker -cannot decrypt *past* messages in a given session (unless past private keys -are retained). 'Perfect forward secrecy' means that no past keys are retained. -'Partial forward secrecy' means that some past key data may be retained. In -other words, when looking **forwards** into the future at a potential -compromise, messages sent prior to the compromise will be secret. - -In Megolm, each recipient maintains a record of the ratchet value which allows them to -decrypt any messages sent in the session after the corresponding point in the -conversation. If this value is compromised, an attacker can similarly decrypt -those past messages. +(also called 'perfect forward secrecy') is the property that if the current +private keys are compromised, an attacker cannot decrypt *past* messages in +a given session. In other words, when looking **forwards** in time towards a +potential future compromise, **current** messages will be secret. + +In Megolm, each recipient maintains a record of the ratchet value which allows +them to decrypt any messages sent in the session after the corresponding point +in the conversation. If this value is compromised, an attacker can similarly +decrypt past messages which were encrypted by a key derived from the +compromised key or any following ratchet values. This gives 'partial' +forrward secrecy. To mitigate this issue, the application should offer the user the option to discard historical conversations, by winding forward any stored ratchet values, |