AES Key Schedule Example

Cryptography Tutorials - Herong's Tutorial Examples

∟Introduction to AES (Advanced Encryption Standard)

∟AES Key Schedule Example

An example of the AES key schedule is provided to illustrate how 11 round keys get calculate from a given 128-bit cipher key.

As an example, let's try to follow the algorithm of the KeyExpansion() procedure, and expand a real cipher key to 11 round keys. This example was presented in the FIPS publication, "Announcing the ADVANCED ENCRYPTION STANDARD (AES)" at http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf in 2001.

Here is the given cipher key in hexadecimal format:
   K = 0x2b7e1516, 0x28aed2a6, 0xabf71588, 0x09cf4f3c

Performing w[0..3] = K:
   w[0] = 0x2b7e1516
   w[1] = 0x28aed2a6
   w[2] = 0xabf71588
   w[3] = 0x09cf4f3c

   temp = w[3]:         0x09cf4f3c

for i = 4: 
   RotWord(temp):       0xcf4f3c09
   SubWord(temp):       0x8a84eb01
   temp XOR 0x01000000: 0x8b84eb01
   temp XOR w[0]:       0xa0fafe17
   w[4] = 0xa0fafe17
   
for i = 5: 
   temp XOR w[1]:       0x88542cb1
   w[5] = 0x88542cb1
   
for i = 6: 
   temp XOR w[2]:       0x23a33939
   w[6] = 0x23a33939

for i = 7: 
   temp XOR w[3]:       0x2a6c7605
   w[7] = 0x2a6c7605
   
for i = 8: 
   RotWord(temp):       0x6c76052a
   SubWord(temp):       0x50386be5
   temp XOR 0x02000000: 0x52386be5
   temp XOR w[4]:       0xf2c295f2
   w[8] = 0xf2c295f2

for i = 9: 
   temp XOR w[5]:       0x7a96b943
   w[9] = 0x7a96b943
   
for i = 10: 
   temp XOR w[6]:       0x5935807a
   w[10] = 0x5935807a

for i = 11: 
   temp XOR w[7]:       0x7359f67f
   w[11] = 0x7359f67f

for i = 12: 
   RotWord(temp):       0x59f67f73
   SubWord(temp):       0xcb42d28f
   temp XOR 0x04000000: 0xcf42d28f
   temp XOR w[8]:       0x3d80477d
   w[12] = 0x3d80477d

for i = 13: 
   temp XOR w[9]:       0x4716fe3e
   w[13] = 0x4716fe3e
   
for i = 14: 
   temp XOR w[10]:      0x1e237e44
   w[14] = 0x1e237e44

for i = 15: 
   temp XOR w[11]:      0x6d7a883b
   w[15] = 0x6d7a883b

for i = 16: 
   RotWord(temp):       0x7a883b6d
   SubWord(temp):       0xdac4e23c
   temp XOR 0x08000000: 0xd2c4e23c
   temp XOR w[12]:      0xef44a541
   w[16] = 0xef44a541
      
for i = 17: 
   temp XOR w[13]:      0xa8525b7f
   w[17] = 0xa8525b7f
   
for i = 18: 
   temp XOR w[14]:      0xb671253b
   w[18] = 0xb671253b
   
for i = 19: 
   temp XOR w[15]:      0xdb0bad00
   w[19] = 0xdb0bad00

for i = 20: 
   RotWord(temp):       0x0bad00db
   SubWord(temp):       0x2b9563b9
   temp XOR 0x10000000: 0x3b9563b9
   temp XOR w[16]:      0xd4d1c6f8
   w[20] = 0xd4d1c6f8
   
for i = 21: 
   temp XOR w[17]:      0x7c839d87
   w[21] = 0x7c839d87

for i = 22: 
   temp XOR w[18]:      0xcaf2b8bc
   w[22] = 0xcaf2b8bc

for i = 23: 
   temp XOR w[19]:      0x11f915bc
   w[23] = 0x11f915bc

for i = 24: 
   RotWord(temp):       0xf915bc11
   SubWord(temp):       0x99596582
   temp XOR 0x20000000: 0xb9596582
   temp XOR w[20]:      0x6d88a37a
   w[24] = 0x6d88a37a

for i = 25: 
   temp XOR w[21]:      0x110b3efd
   w[25] = 0x110b3efd

for i = 26: 
   temp XOR w[22]:      0xdbf98641
   w[26] = 0xdbf98641

for i = 27: 
   temp XOR w[23]:      0xca0093fd
   w[27] = 0xca0093fd

for i = 28: 
   RotWord(temp):       0x0093fdca
   SubWord(temp):       0x63dc5474
   temp XOR 0x40000000: 0x23dc5474
   temp XOR w[24]:      0x4e54f70e
   w[28] = 0x4e54f70e

for i = 29: 
   temp XOR w[25]:      0x5f5fc9f3
   w[25] = 0x5f5fc9f3

for i = 30: 
   temp XOR w[26]:      0x84a64fb2
   w[26] = 0x84a64fb2

for i = 31: 
   temp XOR w[27]:      0x4ea6dc4f
   w[31] = 0x4ea6dc4f

for i = 32: 
   RotWord(temp):       0xa6dc4f4e
   SubWord(temp):       0x2486842f
   temp XOR 0x80000000: 0xa486842f
   temp XOR w[28]:      0xead27321
   w[32] = 0xv

for i = 33: 
   temp XOR w[29]:      0xb58dbad2
   w[33] = 0xb58dbad2

for i = 34: 
   temp XOR w[30]:      0x312bf560
   w[34] = 0x312bf560

for i = 35: 
   temp XOR w[31]:      0x7f8d292f
   w[35] = 0x7f8d292f

for i = 36: 
   RotWord(temp):       0x8d292f7f
   SubWord(temp):       0x5da515d2
   temp XOR 0x1b000000: 0x46a515d2
   temp XOR w[32]:      0xac7766f3
   w[36] = 0xac7766f3

for i = 37: 
   temp XOR w[33]:      0x19fadc21
   w[33] = 0x19fadc21

for i = 38: 
   temp XOR w[34]:      0x28d12941
   w[38] = 0x28d12941

for i = 39: 
   temp XOR w[35]:      0x575c006e
   w[39] = 0x575c006e

for i = 40: 
   RotWord(temp):       0x5c006e57
   SubWord(temp):       0x4a639f5b
   temp XOR 0x36000000: 0x7c639f5b
   temp XOR w[36]:      0xd014f9a8
   w[40] = 0xd014f9a8

for i = 41: 
   temp XOR w[37]:      0xc9ee2589
   w[41] = 0xc9ee2589

for i = 42: 
   temp XOR w[38]:      0xe13f0cc8
   w[42] = 0xe13f0cc8

for i = 43: 
   temp XOR w[39]:      0xb6630ca6
   w[43] = 0xb6630ca6

Building 11 round keys from w[]
   k[ 0] = 0x2b7e1516, 0x28aed2a6, 0xabf71588, 0x09cf4f3c
   k[ 1] = 0xa0fafe17, 0x88542cb1, 0x23a33939, 0x2a6c7605
   k[ 2] = 0xf2c295f2, 0x7a96b943, 0x5935807a, 0x7359f67f
   k[ 3] = 0x3d80477d, 0x4716fe3e, 0x1e237e44, 0x6d7a883b
   k[ 4] = 0xef44a541, 0xa8525b7f, 0xb671253b, 0xdb0bad00
   k[ 5] = 0xd4d1c6f8, 0x7c839d87, 0xcaf2b8bc, 0x11f915bc
   k[ 6] = 0x6d88a37a, 0x110b3efd, 0xdbf98641, 0xca0093fd
   k[ 7] = 0x4e54f70e, 0x5f5fc9f3, 0x84a64fb2, 0x4ea6dc4f
   k[ 8] = 0xead27321, 0xb58dbad2, 0x312bf560, 0x7f8d292f
   k[ 9] = 0xac7766f3, 0x19fadc21, 0x28d12941, 0x575c006e
   k[10] = 0xd014f9a8, 0xc9ee2589, 0xe13f0cc8, 0xb6630ca6