Project 1 (AES)

Objectives

Gain a concrete understanding of the Advanced Encryption Standard (AES) by implementing it for 128, 192, and 256 bit keys.

Gain experience implementing a system from a specification. You may find some areas of the specification difficult to understand. We encourage you to study the specification carefully. Discuss it with other students, the TA, or the instructor. Be tenacious. You will need to study the language-independent specification and implement the standard in your chosen operating system and programming language. You will have to deal with factors such as byte order, signed and unsigned datatypes, etc.

Resources

FIPS Publication 197 is the official standard for AES. Each section in the requirement below will reference the appropriate section in this document.

Wikipedia has a nice overview of AES

There is also a self executing flash animation for Windows OS that illustrates how AES works. (Watch AES flash in your web browser)

Passoff Requirements:

  1. Programming language: You may implement your solution for this project in any language in which you are confident you can implement all necessary functions and can demonstrate portions of your solution to the TA using a debugger.
  2. To receive full credit, you must implement the system using only the resources listed above. You must avoid looking at any AES source code, which will limit your learning experience.
  3. To pass off, you will show the TA that you can correctly encrypt and decrypt ALL of the test cases in Appendix C of the FIPS specification. Additionally, you should print out the debug information for each round as seen in Appendix C.
  4. Sign up on the passoff signup sheet, and Come to 1154 TMCB to pass off.
  5. Submit a file with your source code to Learning Suite

Helpful Notes:

  • Finite Fields are a mathematical concept. They consist of a set, an addition (+) operator, and a multiplication (*) operator. However, + and * can be defined as anything, and may not be the same addition and multiplication that we are familiar with. In the case of AES, whenever you read the term “finite field,” just think of a byte (8-bits, unsigned). The way that we do addition and multiplication on the field will be defined in the document.
  • Review of Binary Operators: C, C++ and Java have operators (&, |, ^, < <, ») to perform simple bitwise operations, such as a bit-wise AND, OR, XOR, left shifts and right shifts respectively. Notice that we use a single & and | instead of the double && and || that we use when doing boolean operations. For a more detailed review, click here.
  • Variable Glossary: There are several variables that are used throughout the document to represent different things. Before you begin, it may be helpful to read through section 2.2 in the FIPS document. In particular, you will need to know the following variables:
     * Nb - The number of words in the block (Nb is always 4)
     * Nk - The number of words in the key (key bit-length / 32)
     * Nr - The number of rounds in the cipher algorithm
  • To see the correct values for these variables using 128, 192 and 256 bit encryption, read the beginning of section 5.
  • The State: AES is a type of block cryptography. This means that the encryption and decryption happens on an entire block at a time, rather than on a single character. In the FIPS document, the block that we are working on is called the state. When you see the word state, think of the block of bytes that you are encrypting.
  • Block Orientation: The state consists of 16 bytes, and is often shown in the document as a 4×4 grid. Be aware that the bytes are ordered going down first, then moving right. For example, the byte[] {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16} would be shown in the document as:
1	5	9	13
2	6	10	14
3	7	11	15
4	8	12	16

Requirements:

  • The AES algorithm makes use of finite field arithmetic. As such, it is important to read and understand Section 4. In particular you should implement:
  1. ffAdd() - adds two finite fields (see Section 4.1)
  2. xtime() - multiplies a finite field by x (see Section 4.2.1)
  3. ffMultiply() - uses xtime to multiply any finite field by any other finite field. (see Section 4.2.1)
  • Implement Key Expansion. Notice that the key for use with this algorithm is given as a byte[], but both cipher and invCipher require a word[] as input. The key expansion algorithm (see Section 5.2) performs this conversion. Appendix A gives excellent examples of the Key expansion algorithm. The following two functions are needed by this algorithm:
  1. subWord() - takes a four-byte input word and substitutes each byte in that word with its appropriate value from the S-Box. The S-box is provided (see Section 5.1.1)
  2. rotWord() - performs a cyclic permutation on its input word.

Key expansion also uses the round constant word array. This array can be generated using xtime(), but is provided here for your convenience.

Rcon[] = { 0x00000000, // Rcon[] is 1-based, so the first entry is just a place holder 
0x01000000, 0x02000000, 0x04000000, 0x08000000, 
0x10000000, 0x20000000, 0x40000000, 0x80000000, 
0x1B000000, 0x36000000, 0x6C000000, 0xD8000000, 
0xAB000000, 0x4D000000, 0x9A000000, 0x2F000000, 
0x5E000000, 0xBC000000, 0x63000000, 0xC6000000, 
0x97000000, 0x35000000, 0x6A000000, 0xD4000000, 
0xB3000000, 0x7D000000, 0xFA000000, 0xEF000000, 
0xC5000000, 0x91000000, 0x39000000, 0x72000000, 
0xE4000000, 0xD3000000, 0xBD000000, 0x61000000, 
0xC2000000, 0x9F000000, 0x25000000, 0x4A000000, 
0x94000000, 0x33000000, 0x66000000, 0xCC000000, 
0x83000000, 0x1D000000, 0x3A000000, 0x74000000, 
0xE8000000, 0xCB000000, 0x8D000000}

If you want to test your key expansion, the spec provides some examples of the workings of a proper key expansion. If you would like to see the same information for another key, try this page.

  • Implement the cipher function. The cipher function is specified in Section 5.1, and an example is given in appendix B. Its implementation is quite simple once the following four transformations are created:
  1. subBytes() - This transformation substitutes each byte in the State with its corresponding value from the S-Box.
  2. shiftRows() - This transformation performs a circular shift on each row in the State (see Section 5.1.2)
  3. mixColumns() - This transformation treats each column in state as a four-term polynomial. This polynomial is multiplied (modulo another polynomial) by a fixed polynomial with coefficients (see Sections 4.3 and 5.1.3).
  4. addRoundKey() - This transformation adds a round key to the State using XOR.
  • Implement the invCipher function. This function is specified in Section 5.3. It reverses the effect of the cipher function. Its implementation is quite simple once the following three transformations are created:
  1. invSubBytes() - This transformation substitutes each byte in the State with its corresponding value from the inverse S-Box, thus reversing the effect of a subBytes() operation.
  2. invShiftRows() - This transformation performs the inverse of shiftRows() on each row in the State (see Section 5.3.1)
  3. invMixColumns() - This transformation is the inverse of mixColumns (see Section 5.3.3).
 Sbox = {
	{ 0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76 } ,
	{ 0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0 } ,
	{ 0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15 } ,
	{ 0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75 } ,
	{ 0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84 } ,
	{ 0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf } ,
	{ 0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8 } ,
	{ 0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2 } ,
	{ 0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73 } ,
	{ 0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb } ,
	{ 0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79 } ,
	{ 0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08 } ,
	{ 0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a } ,
	{ 0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e } ,
	{ 0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf } ,
	{ 0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 }
	}; 
 InvSbox = {
	{ 0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb } ,
	{ 0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb } ,
	{ 0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e } ,
	{ 0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25 } ,
	{ 0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92 } ,
	{ 0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84 } ,
	{ 0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06 } ,
	{ 0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b } ,
	{ 0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73 } ,
	{ 0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e } ,
	{ 0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b } ,
	{ 0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4 } ,
	{ 0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f } ,
	{ 0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef } ,
	{ 0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61 } ,
	{ 0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d }
	};
cs-465/project-1-aes.txt · Last modified: 2017/01/13 19:37 by arcoh
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