25-08-2012, 11:42 AM
Data Encryption Standard - DES
DES presentation.pptx (Size: 103.81 KB / Downloads: 41)
What is Encryption? And why needed?
A message in its original form (plaintext) is converted (encrypted) into an unintelligible form (cipher text) by a set of procedures known as an encryption algorithm (cipher) and a variable, called a key.
The cipher text is transformed (decrypted) back into plaintext using the encryption algorithm and a key.
Encryption has long been used by militaries and governments to facilitate secret communication. It is now commonly used in protecting information within many kinds of civilian systems. Just for example password protection.
DATA ENCRYPTION STANDARD
DES is a system of encryption that takes a fixed-length string (64 bits) of plaintext bits and transforms it through a series of complicated operations into another cipher text of the same length (64 bits).
Its purpose is to provide a standard method for protecting sensitive commercial and unclassified data.
IBM created the first draft of the algorithm, calling it LUCIFER. DES officially became a federal standard in November of 1976.
GENERATION OF 64 bits PLAINTEXT
for example I have the plain text “What is your name”
The hexadecimal conversion for this is "596F7572206C6970 732061726520736D 6F“ a total of 136 bits.
Now this is converted to a code that contains 64x bits number, this is done by adding that number of zeros.
Now each block of 64 bits block is separated such that we get x number of blocks and then each block is individually encrypted.
Here we 64*3=192. i.e. add 192-136=56 zeros.
DES Modes of Operation
The DES algorithm turns a 64-bit message block M into a 64-bit cipher block C. If each 64-bit block is encrypted individually, then the mode of encryption is called Electronic Code Book (ECB) mode. There are two other modes of DES encryption, namely Chain Block Coding (CBC) and Cipher Feedback (CFB), which make each cipher block dependent on all the previous messages blocks through an initial XOR operation.
DES presentation.pptx (Size: 103.81 KB / Downloads: 41)
What is Encryption? And why needed?
A message in its original form (plaintext) is converted (encrypted) into an unintelligible form (cipher text) by a set of procedures known as an encryption algorithm (cipher) and a variable, called a key.
The cipher text is transformed (decrypted) back into plaintext using the encryption algorithm and a key.
Encryption has long been used by militaries and governments to facilitate secret communication. It is now commonly used in protecting information within many kinds of civilian systems. Just for example password protection.
DATA ENCRYPTION STANDARD
DES is a system of encryption that takes a fixed-length string (64 bits) of plaintext bits and transforms it through a series of complicated operations into another cipher text of the same length (64 bits).
Its purpose is to provide a standard method for protecting sensitive commercial and unclassified data.
IBM created the first draft of the algorithm, calling it LUCIFER. DES officially became a federal standard in November of 1976.
GENERATION OF 64 bits PLAINTEXT
for example I have the plain text “What is your name”
The hexadecimal conversion for this is "596F7572206C6970 732061726520736D 6F“ a total of 136 bits.
Now this is converted to a code that contains 64x bits number, this is done by adding that number of zeros.
Now each block of 64 bits block is separated such that we get x number of blocks and then each block is individually encrypted.
Here we 64*3=192. i.e. add 192-136=56 zeros.
DES Modes of Operation
The DES algorithm turns a 64-bit message block M into a 64-bit cipher block C. If each 64-bit block is encrypted individually, then the mode of encryption is called Electronic Code Book (ECB) mode. There are two other modes of DES encryption, namely Chain Block Coding (CBC) and Cipher Feedback (CFB), which make each cipher block dependent on all the previous messages blocks through an initial XOR operation.