Secure communication
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This document provides an overview of popular encryption algorithms. It discusses both symmetric and asymmetric ciphers such as the one-time pad, stream ciphers like A5/1, symmetric block ciphers including DES, 3DES and AES, and asymmetric ciphers RSA and elliptic curve cryptography. It also covers block cipher modes of operation like ECB, CBC, OFB, CFB and CTR. The one-time pad requires truly random keys of the same length as plain text but is impractical. AES with 128-256 bit keys is now secure standard, while DES and 3DES are insecure due to small key sizes. RSA uses 1024-4096 bit keys but is slower than elliptic curve cryptography which provides equivalent security with smaller
Secure communication
- 1. Secure communication Most popular encryption algorithms overview
- 2. Agenda One-time pad Stream ciphers A5/1 Symmetric block ciphers DES (weak), 3DES (secure), AES (secure) Asymmetric block ciphers RSA (slow) Elliptic curves (fast)
- 3. One-time pad Main features: Totally secure crypto technic A key has to be the same length as a plain text A key has to be truly random XOR operation is often used to combine a key and a text Impractical in most cases due to the above key length requirement
- 4. Stream ciphers Inspiration from the one-time pad Types: synchronous self-synchronizing LFSR (linear feedback shift registers)
- 5. A5/1 stream cipher Features: Used in GSM networks 114 bit length keystream Based on three LSFRs Successful attacks exist
- 6. DES DES, Data Encryption Standard, was developed in the 1970s at IBM and based on design of Horst Feistel. It is a symmetric-key algorithm based on Feistel network. Key size is 56 bits only and it is considered insecure now.
- 7. 3DES 3DES - Triple DES Brute force attack on 2DES can use “meet in the middle” technique. It is a symmetric-key algorithm based on Feistel network. Key size is 168 bits only and it is considered insecure now.
- 8. AES AES, Advanced Encryption Standard, established in 2001 by the NIST and based on design of Joan Daemen and Vincent Rijmen. It is a symmetric-key algorithm based on Galois field. Supported key sizes are 128, 192 or 256 bits.
- 9. Block cipher modes A mode of operation is used to encrypt more than one block of plain data. The following is the list of some popular modes: ECB - Electronic Codebook - the simplest mode CBC - Cipher Block Chaining OFB - Output Feedback - makes a synchronous stream cipher CFB - Cipher Feedback - makes a self-synchronizing stream cipher CTR - Counter - makes a synchronous stream cipher
- 10. RSA RSA, described in 1977, was called after its inventors Ron Rivest, Adi Shamir, and Leonard Adleman. It is a public key algorithm. Key size could be in range of 1024 to 4096 bits It is a relatively slow algorithm and usually used to share keys for symmetric algorithms.
- 11. Elliptic curve cryptography It is based on the algebraic structure of elliptic curves. This is the fastest public key algorithm as of now. 256 bit ECC public key provides security compared to 3072 bit RSA public key.
- 12. References Introduction to Cryptography by Christof Paar Cryptography and Computer Privacy
- 13. My blog Learning Network Programming