DKG share index uses uint32, but the tbls scheme uses 16bit

[CluEleSsUK]

Here in the tBLS signing (which is used for partial signatures) the index is a 16bit int:

kyber/sign/tbls/tbls.go

Line 90 in f864ea9

if len(signature) != s.sigGroup.PointLen()+2 {

Throughout the DKG, a uint32 is used:

kyber/share/dkg/structs.go

Line 65 in f864ea9

type DistKeyShare struct {

I haven't actually seen this break anything, but maybe it's a limit for large DKGs!

[CluEleSsUK]

It's possibe the indexes are distinct and I've also misunderstood though - open to education (maybe the 16bit one is just for coefficients?)

[sylvainpelissier]

I think you should use the same type for both. If the user is able to choose their own identifier then they could choose a 2^16 which will be converted to zero by the Sign function which may lead further computation errors during the Recover computation. @bbjubjub2494 highlighted this behavior during the recent LakeCTF.