5. What ‘s Cryptography?
Cryptography is the science
of using mathematics to
encrypt and decrypt data.
Cryptography enables you to
store sensitive information or
transmit it across insecure
networks (like the Internet) so
that it cannot be read by
anyone except the intended
recipient.
6. 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
9. 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
12. Symmetric Algorithm
1. Block Ciphers
• Encrypt data one block at a time (typically 64 bits, or 128 bits)
• Used for a single message
2. 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
13. Block Cipher
• Divide input bit stream into n-bit sections, encrypt only that section, no
dependency/history between sections
15. Mod of Operation
Modes of operation is the procedure of enabling the repeated
and secure use of a block cipher under a single key
Mod of Operation Type:
• CBC (Cipher Block Chaining).
• ECB (Electronic Code Book).
• Propagating cipher-block chaining (PCBC)
• Cipher feedback (CFB)
• Output feedback (OFB)
• Counter (CTR)
18. 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
19. Padding PKCS7
Padding is in whole bytes. The value of each added byte is the
number of bytes that are added.
22. Asymmetric Algorithm
• A user has two keys: a public key and a private
key.
• A message can be encrypted with the public key
and decrypted with the private key to provide
security.
23. RSA
In RSA, e and n are announced to the
public; d and Φ are kept secret.
26. Hashing
• Hashing is an irreversible process with
no keys, the clear message is the only
input for the hashing process
• Its role is to
ensure the integrity
of a message