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--- pgpfan:pgpauth [2025/10/10 21:47] – [PGP Authentication Doesn't Work This Way] Better structure. b.walzer
+++ pgpfan:pgpauth [2025/10/10 22:01] (current) – [The PGP OCFB-MDC Encryption Mode] What sort of implementations? b.walzer
@@ Line 77: / Line 77: @@
 =====The PGP OCFB Encryption Mode=====
-The very existence of this mode seems to confuse people((The PGP OCFB mode is contained in the OpenPGP Symmetrical Encryption Data packet (SED).)). It is a mode with, you guessed it, no integrity check. It is pure encryption. We should have a pretty good idea at this point about why it exists. Since PGP authentication is done directly on the data there is simply no need for anything else. An encryption mode that provided an integrity check feature would be redundant and would cause inefficiency.
+This is an encryption mode with no integrity check((The PGP OCFB mode is contained in the OpenPGP Symmetrical Encryption Data packet (SED).)). It is pure encryption. We should have a pretty good idea at this point why it exists. Since PGP authentication is done directly on the data there is simply no need for an integrity check. An encryption mode that provided an integrity check feature would be redundant and would cause inefficiency.
+The very existence of this mode seems to confuse people...
 =====The PGP OCFB-MDC Encryption Mode=====
-So there is a PGP encryption mode //with// an integrity check((The PGP OCFB-MDC mode is contained in the OpenPGP Symmetrical Encryption Integrity Protected Data packet (SEIPD).)). For those of us who know how PGP authentication works the existence of //this// mode is confusing.
+So... This is awkward...
+OCFB-MDC is a PGP encryption mode //with// an integrity check((The PGP OCFB-MDC mode is contained in the OpenPGP Symmetrical Encryption Integrity Protected Data packet (SEIPD).)). For those of us who know how PGP authentication works the existence of //this// mode is confusing.
 People were happily and securely using the OCFB encryption mode with PGP authentication for many years. The OCFB-MDC mode came along later.
-A valid OCFB-MDC integrity check insures:
+A valid OCFB-MDC integrity check ensures:
   - The file/message has not been modified.
@@ Line 93: / Line 97: @@
 So why does the OCFB-MDC encryption mode exist at all? It's specifically for the case of anonymous (unsigned, unauthenticated) files/messages. We won't know where the file/message came from, but at least we know it wasn't tampered with. It's better than nothing.
-In practice almost all implementations will emit OCFB-MDC encrypted messages even if the file/message is signed. That makes it so that schemes that depend on the integrity check will always have it available without consideration of the authentication status of the message. The resulting inefficiency is apparently considered an acceptable cost. Those implementations that do not require the integrity check can simply just ignore it.
+In practice almost all PGP implementations will emit OCFB-MDC encrypted messages even if the file/message is signed. That makes it so that schemes that depend on the integrity check will always have it available without consideration of the authentication status of the message. The resulting inefficiency is apparently considered an acceptable cost. Those implementations that do not require the integrity check can simply just ignore it.
 When working with PGP, it is important to clearly understand the difference between authentication and the integrity check. The integrity check is limited and often full authentication is required or more desirable.