Today, Mr. Zaki teaches about the modern cryptography. Modern cryptography is different from classic cryptography that taught last lecture. This is because modern cryptography is use a sequence of binary digits (bits) that is, zeros and ones such as ASCII. This bit sequence representing the plain text is then encrypted to give the cipher text as a bit sequence.
Modern cryptography algorithms consist of various types such as stream ciphers and block ciphers. Stream ciphers where the sequence is encrypted bit-by-bit. While block ciphers where the sequence is divided into blocks of a predetermined size. ASCII requires 8 bits to represent one character, and so for a block cipher that has 64-bit blocks, the encryption algorithms acts on eight characters at once.
Since most modern algorithms operate on binary string so we need to be familiar with a method of combining two bits called Exclusive OR and ofter written as XOR. Table below show that the way of doing the XOR. When 0 XOR with 0 will get 0 while 0 XOR with 1 will get 1.
How we encrypt using the modern cryptography? If the plain text is 1100101 and the key stream is 1000110 then by applying the XOR gives 0100011 as the cipher text.
Above table show that the ASCII table and description. How this ASCII table can help in modern cryptography? First, select a plain text and key stream. In this case, I select APPLE as my plain text while my key stream is KEY. Both of the plain text and key stream change to the binary sequence in order to use the XOR.
From the above ASCII table, A uppercase is decimal number 65 while P uppercase is decimal number 80. Follow the ASCII table; we can get the information as below:
Next, we can do the encryption. XOR with plain text and key stream then we can get the cipher text.
Next, Mr. Zaki teaches us about the DES. DES stands for Data Encryption Standards. It is a widely used encryption scheme. The plain text is divided into 64 bit blocks with a key of 56 bits (with 8 bit parity). DES must process through 16 round of Expansion, substitution, key mixing and permutation process. Figure below show that the process of DES.
In the end of the class, Mr. Zaki shows us the process of DES by using flash. However, I still don't know how to do the DES. Maybe it is because I just learn the theory. not yet do it myself.
Modern cryptography algorithms consist of various types such as stream ciphers and block ciphers. Stream ciphers where the sequence is encrypted bit-by-bit. While block ciphers where the sequence is divided into blocks of a predetermined size. ASCII requires 8 bits to represent one character, and so for a block cipher that has 64-bit blocks, the encryption algorithms acts on eight characters at once.
Since most modern algorithms operate on binary string so we need to be familiar with a method of combining two bits called Exclusive OR and ofter written as XOR. Table below show that the way of doing the XOR. When 0 XOR with 0 will get 0 while 0 XOR with 1 will get 1.
How we encrypt using the modern cryptography? If the plain text is 1100101 and the key stream is 1000110 then by applying the XOR gives 0100011 as the cipher text.
Above table show that the ASCII table and description. How this ASCII table can help in modern cryptography? First, select a plain text and key stream. In this case, I select APPLE as my plain text while my key stream is KEY. Both of the plain text and key stream change to the binary sequence in order to use the XOR.From the above ASCII table, A uppercase is decimal number 65 while P uppercase is decimal number 80. Follow the ASCII table; we can get the information as below:
Next, we can do the encryption. XOR with plain text and key stream then we can get the cipher text.
Next, Mr. Zaki teaches us about the DES. DES stands for Data Encryption Standards. It is a widely used encryption scheme. The plain text is divided into 64 bit blocks with a key of 56 bits (with 8 bit parity). DES must process through 16 round of Expansion, substitution, key mixing and permutation process. Figure below show that the process of DES.
In the end of the class, Mr. Zaki shows us the process of DES by using flash. However, I still don't know how to do the DES. Maybe it is because I just learn the theory. not yet do it myself.
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