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Bài giảng Mật mã học: Public-Key cryptography - Huỳnh Trọng Thưa

Bài giảng "Mật mã học: Public-Key cryptography" cung cấp cho người học các kiến thức: Principles of asymmetric cryptography, one-way function, key lengths and security levels, euclidean algorithm, .Mời các bạn cùng tham khảo. | Bài giảng Mật mã học Public-Key cryptography - Huỳnh Trọng Thưa Public-Key Cryptography Huỳnh Trọng Thưa htthua@ptithcm.edu.vn Symmetric vs. Asymmetric Cryptography 1. The same secret key is used for encryption and decryption. 2. The encryption and decryption function are very similar in the case of DES they are essentially identical . Shortcomings Key Distribution Problem Number of Keys n n-1 2 No Protection Against Cheating by Alice or Bob nonrepudiation 2 Principles of Asymmetric Cryptography The crucial part is that Bob the receiver can only decrypt using a secret key. Bob s key k consists of two parts a public part kpub and a private one kpr. 3 Basic key transport protocol with AES as an example of a symmetric cipher Asymmetric schemes of practical relevance are all built from one common principle the one-way function. 4 One-way function Two popular one-way functions the integer factorization problem RSA the discrete logarithm problem Elliptic Curve 5 Main Security Mechanisms of Public-Key Algorithms Key Establishment establishing secret keys overan insecure channel. Diffie-Hellman key exchange or RSA key transport protocols. Nonrepudiation providing nonrepudiation and message integrity Digital signature algorithms RSA DSA or ECDSA. Identification identify entities using challenge-and- response protocols together with digital signatures Smart cards for banking or for mobile phones. Encryption encrypt messages using algorithms such as RSA or Elgamal. 6 Authenticity of Public Keys Do we really know that a certain public key belongs to a certain person this issue is often solved with what is called certificates Public-key algorithms require very long keys resulting in slow execution times. 7 Public-Key Algorithm Families of Practical Relevance Integer-Factorization Schemes RSA. Discrete Logarithm Schemes finite fields Diffie-Hellman key exchange Elgamal encryption or the Digital Signature Algorithm DSA . Elliptic Curve EC Schemes A generalization of the discrete .