pgpfan:authenticated
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pgpfan:authenticated [2021/12/15 23:51] – Made this more effective to better support other articles b.walzer | pgpfan:authenticated [2023/02/28 16:46] (current) – new point b.walzer | ||
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It is sometimes said OpenPGP does not support a feature called [[wp> | It is sometimes said OpenPGP does not support a feature called [[wp> | ||
- | AE is often seen in the case of stateful connected protocols. | + | AE is often seen in the case of stateful connected protocols |
{{auth_stateful_keys.svg}} | {{auth_stateful_keys.svg}} | ||
- | The authorization | + | The authentication |
The entities can then send messages encrypted with the shared key over the connection indefinitely: | The entities can then send messages encrypted with the shared key over the connection indefinitely: | ||
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{{auth_stateful_ae.svg}} | {{auth_stateful_ae.svg}} | ||
- | The authenticated encryption ensures that these messages are from the other entity and were not modified in transit. | + | The authenticated encryption ensures that these messages are from the other entity and were not modified in transit. |
Now we switch to the case of a protocol suitable for offline applications such as encrypted email or stored files. Here is how this is normally done using OpenPGP: | Now we switch to the case of a protocol suitable for offline applications such as encrypted email or stored files. Here is how this is normally done using OpenPGP: | ||
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{{auth_stateless.svg}} | {{auth_stateless.svg}} | ||
- | Offline applications are by nature stateless with no reverse channel available. A message | + | Offline applications are by nature stateless with no reverse channel available. A message is created and sent off over a network. A file is created and stored to some sort of media. So there is no concept or possibility of an ongoing connection. It is simplest to just cryptographically sign the content directly so this is how OpenPGP does it. As a result, OpenPGP does not need any sort of AE when used in the usual way. |
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+ | Suppose we decided we wanted to do things in the more complicated connection oriented way anyway. Since we would be authenticating the connection, not the message/ | ||
OpenPGP supporting systems are sometimes called on to support the case of unsigned (anonymous) messages/ | OpenPGP supporting systems are sometimes called on to support the case of unsigned (anonymous) messages/ | ||
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Even if authentication is not possible in the anonymous message/ | Even if authentication is not possible in the anonymous message/ | ||
- | There is a sort of philosophical issue here as well. OpenPGP is a definition of a message format. It can't directly specify how things are implemented. Most AE schemes are some sort of encryption with an integrity check bundled in. How bundled the check is would get lost in a mere message format. OpenPGP already defines an integrity check in the form of the [[pgpfan: | + | By the way, the OpenPGP method that invokes the use of AE is symmetrical encryption. This is where the same key is used to encrypt something as well as to decrypt it. In practice this mode is only used to encrypt files that are not going to be moved anywhere. As a result interoperability is unimportant and an interoperability standard like OpenPGP is also less important. It turns out though, that the MDC works as AE in this case. The content and the MDC is encrypted with the symmetrical key and as a result authenticates the content on the basis of that key. So OpenPGP actually //has// authenticated encryption but it doesn' |
+ | |||
+ | There is a sort of philosophical issue here as well. OpenPGP is a definition of a message format. It can't directly specify how things are implemented. Most AE schemes are some sort of encryption with an integrity check bundled in. How bundled the check is would get lost in a mere message format. OpenPGP already defines an integrity check in the form of the [[pgpfan: | ||
Summing up, OpenPGP does not require authenticated encryption for the normal case. For unauthenticated material OpenPGP provides the MDC which is specifically designed for that case. | Summing up, OpenPGP does not require authenticated encryption for the normal case. For unauthenticated material OpenPGP provides the MDC which is specifically designed for that case. |
pgpfan/authenticated.1639612316.txt.gz · Last modified: 2021/12/15 23:51 by b.walzer