Asymmetric encryption

• Asymmetric cryptography is also called "public-key cryptography"

• Public Key: shared with everyone

• Private Key: kept secret

• Both keys have the same length
• Asymmetric keys allow signing and verifying signatures

Encryption & Signing Algorithms

RSA (Rivest-Shamir-Adleman)

• It's based on the difficulty of factoring large prime numbers
• Can be used for encryption and digital signature

• Widely used, but slower and uses large key sizes compared to modern algorithms

• Sizes

• 1024 bits
• 2048 bits (default)
• 3072 bits
• 4096 bits

ssh-keygen -t "rsa" # output both keys (private and public)
openssl genrsa # output private key only (public can be extracted from the private)

• Variations
• RS256 (RSA Signature with SHA-256): for signing only

Signing-only Algorithms

ECDSA (Elliptic Curve Digital Signature Algorithm)

• A variant of DSA, but based on the math of elliptic curves
• Mainly used for digital signatures
• Provides strong security with much smaller keys than RSA

• Very common in modern systems (e.g., TLS certificates, Bitcoin, SSH)

• Variations

• ES256 (ECDSA with SHA-256)

EdDSA (Edwards-curve Digital Signature Algorithm)

• Elliptic curve, but with modern optimizations (Ed25519, Ed448).
• Used in SSH (newer keys), modern cryptocurrencies, OpenPGP.