Security protocols

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References

  • Handbook of applied cryptography
! this book is not always up-to-date ! Some protocols might be broken today (eg. Needham-Schroeder public-key protocol)

Authentication Protocol

using symmetric crypto

using public-key crypto - encrytion

Needham-Schroeder-Lowe protocol (NSL)

References: [1]

  • Vulnerable to MiTM attack — use the NSL variant!

The protocol:

A --> B: P_B(k_1,A)
A <== B: P_A(k_1,k_2)
A --> B: P_B(k_2)

The MiTM attack (via relay):

  • If E can persuade A to start a session with him, he can relay to B and convince B that he is communicating with A.
A --> E      : P_E(k_1,A)
      E --> B: P_B(k_1,A)
A <== E <== B: P_A(k_1,k_2)          # E simply relays B's nonce back to A
A --> E      : P_E(k_2)              # E learns k_2 from A's message
      E --> B: P_B(k_2)              # ... and forwards it to B with B public key

Needham-Schroeder-Lowe protocol (NSL)

References: [2], hac, chap 12, §12.38

  • Don't confuse with the symmetric variant (used in Kerberos).
  • Original version (NS protocol) broken — use this variant instead.

The protocol:

A --> B: P_B(k_1,A)
A <== B: P_A(k_1,k_2,B)
A --> B: P_B(k_2)

using public-key crypto - signature