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7/31/2019 15812_5 Advanced Encryption Standards
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Advanced Encryption Standard
5.1. Evaluation Criteria For AES
The Origins of AES
AES Evaluation
5.2. The AES Cipher
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Origins
Replacement for DES was needed
Theoretical attacks that can break it
Demonstrated exhaustive key search attacks
Can use Triple DES but slow, small block size
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NIST issued a call for a new AES in 1997
15 candidates accepted in Jun 1998
5 candidates were short-listed in Aug 1999
Rijndael was selected as the AES in Oct 2000
Published as FIPS PUB 197 standard in Dec 2001
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AES Evaluation Criteria
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Final criteria:
General security
Ease of software & hardware implementation
Flexibility (in en/decrypt, keying, other factors)
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Advanced Encryption Standard
5.1. Evaluation Criteria For AES
The Origins of AES
AES Evaluation
5.2. The AES Cipher
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The AES Cipher - Rijndael
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Rijndael was designed to have thefollowing characteristics:
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AES Structure
Key Scheduling
Message Encoding
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Example:
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Add Round Key : Initial Round Key
Transformation (For 9 Rounds)
1. Sub Bytes
2. Shift Rows
3. Mix Columns
4. Add Round Keys
Transformation (10th
Round Key)1. Sub Bytes
2. Shift Rows
3. Add Round Keys
AES Structure
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AES Structure
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Example:
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Sub Bytes Table
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Inverse Sub Bytes Table
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Example:
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Example:
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Example:
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Key Expansion
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Firstly, the original 16-byte key is copied into the first 4 words of the expanded
key (i.e, the first 4x4 array of our diagram) as shown below:
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Given:
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=
Circular Shift column 1
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S b B t T bl
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Sub Bytes Table
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Fill rest of the column
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Message EncodingStep: 1 : Initial Round: Add Round Key
X- OR
=
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Message EncodingStep 2 : Transformation
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Message EncodingTransformation : Step 1 : Sub Bytes
Check Each cell of the table in S-BOX table
Input:
Sub Byte Table
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Check all the cells and fill as above said manner
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Message EncodingTransformation : Step 2 : Shift Rows
Input:
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=
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=
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=
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=
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Message EncodingTransformation : Step 3 : Mix Columns
Input:
Constant Matrix:
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(d4* 02)+(bf*03)+(5d*01)+(30*01)
M E di
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Message EncodingTransformation : Step 4 : Add Round Key
Input:
O/p from step 3 of Trans. =
Round 1 Key =
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X-OR
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=
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X-OR
X-OR
X-OR
=
=
=
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Link for animated AEShttp://www.cs.bc.edu/~straubin/cs381-
05/blockciphers/rijndaelingles 2004.swf
Otherwise in google type
animated AES and open first link
http://www.cs.bc.edu/~straubin/cs381-05/blockciphers/rijndaelingles%202004.swfhttp://www.cs.bc.edu/~straubin/cs381-05/blockciphers/rijndaelingles%202004.swfhttp://www.cs.bc.edu/~straubin/cs381-05/blockciphers/rijndaelingles%202004.swfhttp://www.cs.bc.edu/~straubin/cs381-05/blockciphers/rijndaelingles%202004.swfhttp://www.cs.bc.edu/~straubin/cs381-05/blockciphers/rijndaelingles%202004.swf