Changes between Version 12 and Version 13 of NewMutableEncodingDesign

Timestamp:

2010-01-08T02:33:56Z (15 years ago)

Author:

davidsarah

Comment:

added cap examples for K=160, and link to argument about multi-target attacks

NewMutableEncodingDesign

@@ -47 +47 @@
 == Filecap Length ==
 
-A likely security parameter K (=kappa) would be 96 or 128 bits, and most of
-the filecaps will be some multiple of K.
+A likely security parameter K (=kappa) would be 96, 128, or 160 bits, and most of
+the filecaps will be some multiple of K. [96 bits is too short IMHO --David-Sarah]
 
 Assuming a {{{tahoe:}}} prefix and no additional metadata, here's what
@@ -56 +56 @@
   * 96 {{{tahoe:14efs6T5YNim0vDVV}}}
   * 128 {{{tahoe:4V2uIYVX0PcHu9fQrJ3GSH}}}
+  * 160 {{{tahoe:8gdR7Epld72UvkF6Pe9hhT8NQx3}}}
  * 2*K:
   * 192 {{{tahoe:072Og6e75IOP9ZZsbR1Twjs6X5xXJnBAF}}}
   * 256 {{{tahoe:fZeioazoWrO62reiAjzUAyV0uz3ssh6Hnanv8cKMClY}}}
+  * 320 {{{tahoe:j6Re0BbWp7DqJtgd9fUXl4pWiD5kr1mjT9DtudJ72o0vhPen83Utza}}}
  * 3*K:
   * 288 {{{tahoe:11DriaxD9nipA10ueBvv5uoMoehvxgPerpQiXyvMPeiUUdtf6}}}
   * 384 {{{tahoe:3a31SqUbf8fpWE1opRCT3coDhRqTU7bDU2AvC3RQJBu6ZNFhVscyxA9slYtPVT79x}}}
+  * 480 {{{tahoe:P6rGeI6CwlG4i8W2l6haSoC9rfPjw0KHBi8xAk4F8vdhnRhL8nwE27CitJ9Rld06HuKt8VucypJRcbGFo}}}
 
 Adding 2 metadata characters and a clear separator gives us:
@@ -67 +70 @@
  * 96: {{{tahoe:MW-14efs6T5YNim0vDVV}}}
  * 128: {{{tahoe:DW-4V2uIYVX0PcHu9fQrJ3GSH}}}
+ * 160: {{{tahoe:DW-8gdR7Epld72UvkF6Pe9hhT8NQx3}}}
  * 192: {{{tahoe:MR-072Og6e75IOP9ZZsbR1Twjs6X5xXJnBAF}}}
  * 256: {{{tahoe:DR-fZeioazoWrO62reiAjzUAyV0uz3ssh6Hnanv8cKMClY}}}
  * 288: {{{tahoe:MR-11DriaxD9nipA10ueBvv5uoMoehvxgPerpQiXyvMPeiUUdtf6}}}
- * 384: {{{tahoe:MR-3a31SqUbf8fpWE1opRCT3coDhRqTU7bDU2AvC3RQJBu6ZNFhVscyxA9slYtPVT79x}}}
+ * 320: {{{tahoe:MV-j6Re0BbWp7DqJtgd9fUXl4pWiD5kr1mjT9DtudJ72o0vhPen83Utza}}}
+ * 384: {{{tahoe:DV-3a31SqUbf8fpWE1opRCT3coDhRqTU7bDU2AvC3RQJBu6ZNFhVscyxA9slYtPVT79x}}}
+ * 480: {{{tahoe:MV-P6rGeI6CwlG4i8W2l6haSoC9rfPjw0KHBi8xAk4F8vdhnRhL8nwE27CitJ9Rld06HuKt8VucypJRcbGFo}}}
 
 [http://allmydata.org/trac/tahoe/ticket/217#comment:44 #217:c44] says that,
 if we don't need to prevent collisions, then we can use a K-bit hash for
-K-bit second-pre-image resistance.
+K-bit second-pre-image resistance. However, see
+[http://allmydata.org/trac/tahoe/ticket/882#comment:6 #882:c6] for a
+counterargument saying that 50 extra bits or so are needed to be secure
+against multi-target attacks.
 
 = Design Proposals =