Asymmetric Cryptography
Definition
Cryptosystem that uses a key pair: a public key (shareable) and a private key (secret). Built on mathematical trapdoor functions where the forward direction is cheap and the reverse is computationally hard without the trapdoor.
- Key structure
- Public key and private key pair
- Basis
- Trapdoor mathematical functions
- Property
- Forward direction cheap, reverse hard without trapdoor
- Common examples
- RSA, elliptic-curve cryptography
Common questions
Why is asymmetric cryptography central to digital signature verification in forensic casework?+
Because the private key is never shared, a signature that verifies correctly against the corresponding public key demonstrates the signer held that private key at signing time, giving investigators a way to attribute a signed file or message without needing access to any secret.
What makes a trapdoor function different from an ordinary one-way function?+
An ordinary one-way function is hard to reverse for anyone. A trapdoor function is also hard to reverse in general, but becomes easy for someone holding a specific secret, the private key, which is what lets the key holder decrypt or sign while others cannot.
Related terms
- Digital Signature
- Cryptographic proof of authenticity, integrity and non-repudiation. Sign by encrypting a hash of the message with the signer's private key; verify by...
- DSC
- Digital Signature Certificate. An Indian X.509 certificate issued by a CCA-licensed CA. Class 3 is the current mandatory tier for income tax,...
- ECC
- Elliptic Curve Cryptography. Smaller keys for equivalent security; 256-bit ECC is roughly equivalent to 3072-bit RSA. Used in ECDSA signatures, ECDH key...
- Hash Function
- Deterministic function that maps an input of arbitrary length to a fixed-length output. A cryptographic hash adds pre-image resistance, second pre-image resistance,...
- HMAC
- Hash-based Message Authentication Code, RFC 2104. Combines a secret key with a hash function to produce a MAC; immune to the length-extension...
- PKI
- Public Key Infrastructure. The set of roles (CA, RA, VA) and artefacts (X.509 certificates, CRL, OCSP) that bind a public key to...
- RSA
- Rivest-Shamir-Adleman, 1977. Public-key cryptosystem based on the hardness of factoring a product of two large primes. Common sizes today: 2048-bit (standard), 3072-bit...
- Trapdoor Function
- A one-way function with a secret 'trapdoor' that makes the reverse direction tractable. RSA's trapdoor is the factorisation of n into p...