x/crypto/cryptobyte: expose uint48 methods

[hasheddan]

The x/crypto/cryptobyte package currently supports methods on the Builder and String for adding and reading uint8, uint16, uint24, uint32, and uint64 values. uint48 values are useful when working with protocols such as DTLS, which uses a uint48 value for record sequence numbers.

This proposal involves introducing the two following methods:

func (b *Builder) AddUint48(v uint64)

func (s *String) ReadUint48(out *uint64) bool

[seankhliao]

cc @golang/security

[rsc]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group

[FiloSottile]

SGTM, I have implemented them myself at least once.

[hasheddan]

Just noting that there is currently an implementation for this proposal open at golang/crypto#265

[rsc]

Based on the discussion above, this proposal seems like a likely accept.
— rsc for the proposal review group

[rsc]

No change in consensus, so accepted. 🎉
This issue now tracks the work of implementing the proposal.
— rsc for the proposal review group