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This new mask will pre-compute reusable values, speeding up repeated verification and aggregation of aggregate signatures (mostly the former).
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,112 @@ | ||
| package bdn | ||
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| import ( | ||
| "fmt" | ||
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| "github.com/drand/kyber" | ||
| "github.com/drand/kyber/sign" | ||
| ) | ||
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| type Mask interface { | ||
| GetBit(i int) (bool, error) | ||
| SetBit(i int, enable bool) error | ||
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| IndexOfNthEnabled(nth int) int | ||
| NthEnabledAtIndex(idx int) int | ||
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| Publics() []kyber.Point | ||
| Participants() []kyber.Point | ||
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| CountEnabled() int | ||
| CountTotal() int | ||
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| Len() int | ||
| Mask() []byte | ||
| SetMask(mask []byte) error | ||
| Merge(mask []byte) error | ||
| } | ||
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| var _ Mask = (*sign.Mask)(nil) | ||
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| // We need to rename this, otherwise we have a public field named Mask (when we embed it) which | ||
| // conflicts with the function named Mask. It also makes it private, which is nice. | ||
| type maskI = Mask | ||
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| type CachedMask struct { | ||
| maskI | ||
| coefs []kyber.Scalar | ||
| pubKeyC []kyber.Point | ||
| // We could call Mask.Publics() instead of keeping these here, but that function copies the | ||
| // slice and this field lets us avoid that copy. | ||
| publics []kyber.Point | ||
| } | ||
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| // Convert the passed mask (likely a *sign.Mask) into a BDN-specific mask with pre-computed terms. | ||
| // | ||
| // This cached mask will: | ||
| // | ||
| // 1. Pre-compute coefficients for signature aggregation. Once the CachedMask has been instantiated, | ||
| // distinct sets of signatures can be aggregated without any BLAKE2S hashing. | ||
| // 2. Pre-computes the terms for public key aggregation. Once the CachedMask has been instantiated, | ||
| // distinct sets of public keys can be aggregated by simply summing the cached terms, ~2 orders | ||
| // of magnitude faster than aggregating from scratch. | ||
| func NewCachedMask(mask Mask) (*CachedMask, error) { | ||
| return newCachedMask(mask, true) | ||
| } | ||
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| func newCachedMask(mask Mask, precomputePubC bool) (*CachedMask, error) { | ||
| if m, ok := mask.(*CachedMask); ok { | ||
| return m, nil | ||
| } | ||
|
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| publics := mask.Publics() | ||
| coefs, err := hashPointToR(publics) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to hash public keys: %w", err) | ||
| } | ||
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| cm := &CachedMask{ | ||
| maskI: mask, | ||
| coefs: coefs, | ||
| publics: publics, | ||
| } | ||
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| if precomputePubC { | ||
| pubKeyC := make([]kyber.Point, len(publics)) | ||
| for i := range publics { | ||
| pubKeyC[i] = cm.getOrComputePubC(i) | ||
| } | ||
| cm.pubKeyC = pubKeyC | ||
| } | ||
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| return cm, err | ||
| } | ||
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| // Clone copies the BDN mask while keeping the precomputed coefficients, etc. | ||
| func (cm *CachedMask) Clone() *CachedMask { | ||
| newMask, err := sign.NewMask(nil, cm.publics, nil) | ||
| if err != nil { | ||
| // Not possible given that we didn't pass our own key. | ||
| panic(fmt.Sprintf("failed to create mask: %s", err)) | ||
| } | ||
| if err := newMask.SetMask(cm.Mask()); err != nil { | ||
| // Not possible given that we're using the same sized mask. | ||
| panic(fmt.Sprintf("failed to create mask: %s", err)) | ||
| } | ||
| return &CachedMask{ | ||
| maskI: newMask, | ||
| coefs: cm.coefs, | ||
| pubKeyC: cm.pubKeyC, | ||
| publics: cm.publics, | ||
| } | ||
| } | ||
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| func (cm *CachedMask) getOrComputePubC(i int) kyber.Point { | ||
| if cm.pubKeyC == nil { | ||
| // NOTE: don't cache here as we may be sharing this mask between threads. | ||
| pub := cm.publics[i] | ||
| pubC := pub.Clone().Mul(cm.coefs[i], pub) | ||
| return pubC.Add(pubC, pub) | ||
| } | ||
| return cm.pubKeyC[i] | ||
| } |