Schnorr Signatures Study Guide
Introduction
Schnorr Signature is a digital signature scheme named after its inventor, Claus-Peter Schnorr. The scheme is based on the mathematical concept of elliptic curve cryptography and has gained attention for its advantages over other signature schemes, including its efficiency and security.
Elliptic Curve Cryptography
Before diving into Schnorr signatures, it is essential to have a good understanding of elliptic curve cryptography (ECC) since it's the core concept used in the scheme.
Key Pair:
ECC makes use of a pair of keys to work, which are public and private. These keys are essentially a pair of random numbers chosen within the range of a large prime number.
Elliptic Curve:
An elliptic curve is an equation in two variables that describe the surface of a torus. It has a set of points that satisfy the equation and has specific arithmetic properties, resulting in a group of points that have similar cryptographic properties.
Scalar Multiplication:
Scalar multiplication is the operation that is performed on a point and a scalar to generate a new point. The scalar value can be any number picked randomly within a range.
Discrete Logarithm Problem:
ECC's security is based on the concept of the discrete logarithm problem. It is computationally difficult to determine the scalar multiplication used to derive a public key from the private key.
Schnorr Signature
Advantages:
The Schnorr signature scheme has several advantages over other signature schemes, including:
- Security
- Efficiency
- Linearity
- Non-malleability
Signature Generation:
- The signer generates a random number called nonce
k
.
- The signer generates a public key
P
using their private key d
and the scalar multiplication.
- The signer produces a message
m
and calculates e = hash(m)
where hash()
is a hash function.
- The signer calculates
R = k*G
where G
is the generator point of the elliptic curve.
- The signer calculates
S = k + e*d
where d
is the private key.
- The signature is the pair
(R, S)
.
Signature Verification:
- The verifier receives the signature's message, public key, and the signer`
- The verifier calculates
e = hash(m)
where hash()
is a hash function.
- The verifier checks if the coordinates of the point R satisfy the curve's equation and lie in the allowable range.
- The verifier checks if
S*G = R + e*P
, where G
is the generator point of the elliptic curve.
- If the equation is satisfied, the signature is valid; otherwise, it is invalid.
Conclusion:
Schnorr signature is a secure and efficient signature scheme based on the mathematical concept of elliptic curve cryptography. It has gained attention due to its advantages over other signature schemes. Understanding the fundamentals of elliptic curve cryptography is crucial in understanding Schnorr signatures.