Cryptography

• Digital Certificate


  Consists of 2 parts: Plaintext and Same plaintext hashed and digitally signed
• Ways to attack Digital Certificates

  • Convince Digital Certificate Issuer that attacker's public key is the subject's public key
  • Substitute subject's public key with attacker's public key
  • Unauthorized use of issuer's private key
  • Substitute certificate user's public key
• Digital Certificate issuer is trusted by the user of the certificate


  It is dangerous if the Digital Certificate issuer is fraudulent
• Attacker gets issuer's private key


  Unauthorized use of issuer's private key
• Certificate user's private key is intercepted and substituted


  Attacker can substitute user's public key
• If Black Hat can access certificate user's computer, they can substitute the user's public key with someone else's public key
• 2 ways to verify a certificate

  • Consumer or user of the certificate must have a trusted issuer's public key
  • Consumer can then chain from his trusted public key to a trusted copy of the issuer's public key
• Validity of issuer's public key

  • It must be confirmed by a trusted Certificate Authority
• Example of issuing a certificate

  1. Owner's name

  2. Issuer: CA's name

  3. Private Key of CA

  4. Hash Function (MD5/SHA-1)

  5. RSA Encryption

  6. Owner's public key

  7. Validity: lifetime of cert

  8. Signature algorithm

  9. Signature (signed by the CA)
• Example of issuing a certificate

  • Dawn is the Owner, Alice is the CA
• Example of verifying a certificate

  1. Owner's name

  2. Issuer: CA's name

  3. Validity: lifetime of cert

  4. Hash Function (MD5/SHA-1)

  5. Owner's public key

  6. Public key of CA

  7. Signature algorithm

  8. Signature (signed by the CA)

  9. Decryption
• Owner's public key


  Equal to the public key in the certificate