l l l Check Digit Check Sum Hash
- Slides: 54
การตรวจสอบความถกตองของขอมล l l l Check Digit Check Sum Hash Function Message Authentication Code Digital Signature
CHECK DIGIT
CHECK SUM
Error Detection in IP Protocol l IP Check sum Field
ตวอยางการคำนวณ l l l l checksum Packet : 01 00 F 2 03 F 4 F 5 F 6 F 7 00 00 โดย 00 00 = checksum field จดกลมได : 0100 F 203 F 4 F 5 F 6 F 7 รวมตวเลข : 0100 + F 203 + F 4 F 5 + F 6 F 7 = 0002 DEEF ตวสวน Overflow (0002) บวกกบสวนทเหลอ : DEEF + 002 = DEF 1 ทำ 1's complement : ~DEF 1 = 210 E ได checksum = 21 0 E รวมเปนขอมล 01 00 F 2 03 F 4 F 5 F 6 F 7 21 0 E
HASH FUNCTION
Hash Functions 20
Hash Function l ตวอยาง l l l l Hash Function) Message Digest , Secure Hash Algorithm) MD 2 (128 bits) by Ronald Rivests MD 4 (128 bits) by Ronald Rivests MD 5 (128 bits) by Ronald Rivests MD 6 (Variable, 0<d≤ 512 bits) by Ronald Rivests Team SHA 0 (160 bits) by National Security Agency : NSA SHA 1 (160 bits) by National Security Agency : NSA SHA 2 Series (SHA-224, SHA-256, SHA-384, SHA-512) By National Security Agency : NSA
MD 5 l l l คดคนโดย Ronald Rivest (the R in RSA) ผลลพธมขนาด 128 -bit RFC 1321
4. Continued (4 Rounds) Addition (+) is mod 232
Step 4. Continued (Each Round) Addition (+) is mod 232 For each 512 -bit chunk of message break chunk into sixteen 32 -bit littleendian words X[k], 0 ≤ k ≤ 15
Table T l l ตาราง T มคาขอมลทงหมด สรางจาก sine function. l l 64 คา for i from 0 to 63 T[i] : = floor(abs(sin(i + 1)) × (2 pow 32)) 31
Table T 32
Step 4. Round 1 and 2 <<<S = Left bit Rotation by S Space
Step 4. Round 3 and 4 34
MD 5 Boolean Functions l ฟงกชน ของขอมล l l G, H, I, F ทำหนาทเปน X, Y, Z เมอ "bitwise parallel” AND OR NOT XOR F(X, Y, Z) = (X Y) ( X Z) G(X, Y, Z) = (X Z) (Y Z) H(X, Y, Z) = X Y Z I(X, Y, Z) = Y (X Z)
Step 4. Continued 36
ตวอยาง MD 5 function l MD 5("The quick brown fox jumps over the lazy dog") 9 e 107 d 9 d 372 bb 6826 bd 81 d 3542 a 419 d 6 l MD 5("The quick brown fox jumps over the lazy dog. ") e 4 d 909 c 290 d 0 fb 1 ca 068 ffaddf 22 cbd 0 l MD 5("") d 41 d 8 cd 98 f 00 b 204 e 9800998 ecf 8427 e
Other Message Digest Algorithms l l l MD 4 SHA-1 RIPEMD-160 39
A Comparison of MD 5, SHA-1, and RIPEMD-160 40
MESSAGE AUTHENTICATION CODE
Message Authentication Code
Use of a MAC Secret key MAC message Secret key algorithm Unsecured channel message MAC verification algorithm Signer Verifier Ok / not Ok
DIGITAL SIGNATURE
Digital Signatures Scheme l l l Data integrity Message authentication Non-repudiation Signer’s private key Signing message Signer’s public key algorithm Unsecured channel message signature Signature verification algorithm Signer Verifier Ok / not Ok
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