What ‘s Cryptography?Cryptography is the scienceof using mathematics toencrypt and decrypt data.Cryptography enables you tostore sensitive information ortransmit it across insecurenetworks (like the Internet) sothat it cannot be read byanyone except the intendedrecipient.
The Purpose of Cryptography• Authentication: this process to prove the identity of an entity can be based on something you know, such as a password; something you have, such as an encryption key or card; something you are, such as biometric measurements• Privacy/Confidentiality: information is NOT made available or disclosed to unauthorized individuals, entities, or processes• Integrity: This property refers to data that has NOT been changed, destroyed, or lost in an unauthorized or accidental manner.• Non-repudiation: Repudiation is the denial by one of the entities involved in a communication of having participated in all or part of the communication Non-repudiation Authentication : Xác thực người dùng Confidentiality : Bảo mật thông tin Integrity : Toàn vẹn dữ liệu Non-Repudiation : Chống lại sự thoái thác trách nhiệm
Cryptography Methods• Symmetric Same key for encryption and decryption Key distribution problem• Asymmetric Mathematically related key pairs for encryption and decryption Public and private keys Symmetric: Mã hóa đối xứng Asymetric : Mã hóa bất đối xứng
Symmetric Algorithm1. Block Ciphers • Encrypt data one block at a time (typically 64 bits, or 128 bits) • Used for a single message2. Stream Ciphers • Encrypt data one bit or one byte at a time • Used if data is a constant stream of information Block Cipher: Mã hóa khối dữ liệu Stream Cipher: Mã hóa dòng dữ liệu
Block Cipher• Divide input bit stream into n-bit sections, encrypt only that section, no dependency/history between sections
Stream Cipher Stream Cipher
Mod of OperationModes of operation is the procedure of enabling the repeated and secure use of a block cipher under a single keyMod of Operation Type:• CBC (Cipher Block Chaining).• ECB (Electronic Code Book).• Propagating cipher-block chaining (PCBC)• Cipher feedback (CFB)• Output feedback (OFB)• Counter (CTR)
ECB – Electronic Code BookDisadvantage
CBC-Cipher Block Chaining
Padding Each TDES encrypts one block of 64 bits of data. What ‘s happen if PIN size have 30 bits data length ???Padding Scheme: fill additional data to consist data block size.Padding Type:• Bit padding: Byte padding: M 1 0…0 M L…L m bit 1 bit (L – 1) bit m byte L byte
Padding PKCS7Padding is in whole bytes. The value of each added byte is thenumber of bytes that are added.