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use to_bytes in primitive types and reduce serialization size

This commit is contained in:
Alfredo Garcia 2021-05-10 10:02:20 -03:00 committed by Deirdre Connolly
parent 07d8c06ed6
commit 5586bd8aaf
1 changed files with 13 additions and 15 deletions
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rfcs/0001-messages.md
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@ -118,8 +118,8 @@ struct Commitment {
binding: jubjub::AffinePoint,
}
// The aggregator decide what message is going to be signed and
// send it to each participant with all the commitments collected.
// The aggregator decides what message is going to be signed and
// sends it to each participant with all the commitments collected.
struct MsgSigningPackage {
// The number of participants.
participants: u8,
@ -242,21 +242,19 @@ Bytes | Field name | Data type
#### `Scalar`
`Scalar` is a an alias for `jubjub::Fr` and this is a `[u64; 4]` as documented in https://github.com/zkcrypto/jubjub/blob/main/src/fr.rs#L16
`Scalar` is a an alias for `jubjub::Fr`. We use `Scalar::to_bytes` to get a 32-byte little-endian canonical representation. See https://github.com/zkcrypto/bls12_381/blob/main/src/scalar.rs#L252
#### `AffinePoint`
Much of the math in FROST is done using `jubjub::ExtendedPoint`. This is a structure with 5 `jubjub::Fq`s as defined in https://github.com/zkcrypto/jubjub/blob/main/src/lib.rs#L128-L134
Each `Fq` needed to form a `jubjub::ExtendedPoint` are `Scalar`s of `bls12_381` crate. Scalar here is `[u64; 4]` as documented in https://github.com/zkcrypto/bls12_381/blob/main/src/scalar.rs#L16
For message exchange `jubjub::AffinePoint`s are a better choice as they are shorter in bytes, they are formed of 2 `jubjub::Fq` instead of 5: https://github.com/zkcrypto/jubjub/blob/main/src/lib.rs#L70-L73
Much of the math in FROST is done using `jubjub::ExtendedPoint`. But for message exchange `jubjub::AffinePoint`s are a better choice, as their byte representation is smaller.
Conversion from one type to the other is trivial:
https://docs.rs/jubjub/0.6.0/jubjub/struct.AffinePoint.html#impl-From%3CExtendedPoint%3E
https://docs.rs/jubjub/0.6.0/jubjub/struct.ExtendedPoint.html#impl-From%3CAffinePoint%3E
We use `AffinePoint::to_bytes` to get a 32-byte little-endian canonical representation. See https://github.com/zkcrypto/jubjub/blob/main/src/lib.rs#L443
### Payload
Payload part of the message is variable in size and depends on message type.
@ -265,22 +263,22 @@ Payload part of the message is variable in size and depends on message type.
Bytes | Field name | Data type
-------|-------------|-----------
256 | secret_key | Scalar
512 | commitments | AffinePoint
512+32 | group_public| GroupPublic
32 | secret_key | Scalar
32 | commitments | AffinePoint
32+32 | group_public| GroupPublic
#### `MsgCommitments`
Bytes | Field name | Data type
--------|------------|-----------
512+512 | commitment | Commitment
32+32 | commitment | Commitment
#### `MsgSigningPackage`
Bytes | Field name | Data type
-----------------------|----------------|-----------
1 | participants | u8
(1+1024)*partipants | commitments | Vec<CollectedCommitments>
(1+32+32)*partipants | commitments | Vec<CollectedCommitment>
8 | message_length | u64
message_length | message | [u8]
@ -288,13 +286,13 @@ message_length | message | [u8]
Bytes | Field name | Data type
------|------------|-----------
256 | signature | Scalar
32 | signature | Scalar
#### `MsgFinalSignature`
Bytes | Field name | Data type
------|------------------|-----------
64 | final_signature | FinalSignature
32+32 | final_signature | FinalSignature
## Not included