¶ Prerequisites
¶ Digital Signatures
Digital signatures support the basic properties of digital signatures: proof that the:
- message was sent by the person claiming to send it
- message has not been tampered with
Private Key + Message = Signature
Public Key + Message + Signature = Verification
Verification = SPECIFIC message was sent by SPECIFIC sender
¶ BLS Signatures
Boneh–Lynn–Shacham Digital Signatures (BLS signatures) are a specific type of digital signature. BLS signatures function perfectly fine (albeit relatively slowly) as standard cryptographic scheme, but the real magic comes from aggregation.
Aggregation means that given a single message, multiple signatures can be verified with a single operation.
¶ Signature Aggregation
Technically "signatures" represent a specific point in an elliptic curve and can be "added up." This is a (computationally) easy operation.
The final result is also a point in the elliptic curve, and is therefore indistinguishable from a non-aggregated signature.
¶ Public Key Aggregation
Just like a signature, a "public key" is also a point on an elliptic curve and can be similarly "added up" (also computationally easy).
Once again, aggregated public keys are mathematically indistinguishable from non-aggregated public keys.
¶ Aggregated Verification
Since aggregate signatures are indistinguishable from normal signatures, and aggregate public keys are indistinguishable from normal public keys, we can reuse our normal verification algorithm.
Thus, a single operation can verify a huge amount of signatures.
¶ Benefits of Aggregation
As previously mentioned, BLS signatures are computationally expensive when compared to verifying a more standard scheme - more than an order of magnitude slower. However, each verification can count for MUCH more than a standard scheme (a single verification).
Imagine you need to verify 100 signatures:
- Standard digital signature: x time/verification * 100 verifications = 100x
- BLS digital signature: 10x time/verification * 1 verification = 10x
The more signatures you can aggregate, the higher the savings
But verification speed is not the only benefit: BLS signatures offer huge space savings over non-aggregated signatures. An aggregated signatures is the same size as a single signature, regardless of how many signatures have been aggregated.
Imagine you need to verify 100 signatures:
- Standard digital signature: x bytes/signature * 100 signatures = 100x
- BLS digital signature: x bytes/signature * 1 signature = x
More aggregation equals more savings, but even more with space than speed.
BLS signatures are a type of digital signature that provide the same guarantees as any signature (authenticity and liveness) but provide huge scaling benefits when verifying large groups of signatures.
¶ Resources
Source Material - Twitter Link
Source Material - PDF