(1/12) Cryptography 201: BLS Digital Signatures
Digital signatures provide cryptographic assurance that a specific person sent a specific message. Their existence is critical, but traditional digital signatures are not scalable.
A manual for aggregation and acceleration.
(2/12) Boneh–Lynn–Shacham Digital Signatures (BLS signatures) are a specific type of digital signature
BLS signatures support the basic properties of digital signatures: proof that the:
1) message was sent by the person claiming to send it
2) message has not been tampered with
twitter.com/SalomonCrypto/status/1575127511066824704
(3/12) Digital signatures in 1 tweet:
Private Key + Message = Signature
Public Key + Message + Signature = Verification
Verification = SPECIFIC message was sent by SPECIFIC sender
twitter.com/SalomonCrypto/status/1575127521963651076
(4/12) 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.
(5/12) 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.
(6/12) 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.
(7/12) 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.
(8/12) 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).
(9/12) 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
(10/12) 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.
(11/12) 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.
(12/12) 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.
Can you think of anything that uses lots of digital signatures?