On 01/22/2016 03:26 PM, =JeffH wrote: > On 01/22/2016 12:29 PM, =JeffH wrote: >> [ fixed pitch font advised here ] > > the below is corrected to use "byte count" rather than "index" or > "indicies" (and to ditch the tabs).. > > > > On 01/22/2016 09:42 AM, =JeffH wrote: > > > [ resending from different account - my work addr ends up in spam > > > bucket for many it seems ] > > > > > > On 1/20/16, 11:01 AM, "Benjamin Kaduk" <bka...@akamai.com> wrote: > > > >On 01/20/2016 12:47 PM, Hodges, Jeff wrote: > > > >> On 1/13/16, 12:53 PM, "Benjamin Kaduk" <bka...@akamai.com> wrote: > > > >>> On 01/13/2016 02:44 PM, Jong-Shian Wu wrote: > > > >>>> I have a question about the even-vs-odd restrictions on the > > > length of > > > >>>> a valid variable-length vector defined in TLS specification > after > > > >>>> reading the section 4.3 of RFC 5246 [1] which states that: > > > >>>> "The length of an encoded vector must be an even multiple of the > > > >>>>length > > > >>>> of a single element (for example, a 17-byte vector of uint16 > > > would be > > > >>>> illegal)." > > > >>>> > > > >>> It means "whole-number" as opposed to fractional, i.e., there > should > > > >>>not > > > >>> be unused "junk bytes" at the end. > > > >> In case it's helpful, here's a suggested re-write of that quoted > > > >>sentence > > > >> above.. > > > >> > > > >> The length of an encoded variable-length vector must be an > > > >> exact multiple of the length of a single element. For example, > > > >> an encoded 17-byte vector of uint16 would be illegal, and an > > > >> encoded variable-length vector of four 32 byte elements, > > > >> having a ceiling of 2^16-1, will be 130 bytes long overall > > > >> (2 byte length field followed by 128 bytes of data). > > > > > > > >Wouldn't the ceiling more properly be 2^16-4 in that case? > > > > > > hm, I'm not sure -- what would be the rationale? The exact multiple > > > criteria? but 2^16 / 32 = 2048 while (2^16-4) / 32 = 2047.875 > > > > Ah, I seem to have conflated bits and bytes due to reading too quickly > > and should have said (2^16-32), as Ilari alluded to with "or rounding > > thereof to integral multiple of > > elements". > > hm, but in this case it seems that a variable-length vector declared > with a length range of <0..2^16-1> would exactly accommodate up to > 2048 32-byte elements.. > > opaque Foo[32] ; > > Foo fooSequence<0..2^16-1>; /* will accommodate up to 2048 > Foo instances */ > > ..because it has a zero-based byte count, as in this example.. > > > opaque Array<0..2^2-1> ; /* should accommodate > 2^2 = 4 1-byte elements */ > > /* > Array with 4 > elements in memory: [ xx xx xx xx ] > byte count (hex): 0 1 2 3 3 = 2^2-1 > > byte count (binary): 00 01 10 11 > > */ > > > ..yes? or am I missing something?
You are missing something. The encoded length represents the actual number of bytes that will follow, so that a zero-length array with maximum length 2^16-1 is encoded as just 00 00. So, even though the index into the array starts at zero, the actual length "starts at" 1, just like in C. -Ben _______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
