X509 Certificate Structure OID Represenation of AlgorithmIdentifier

1. X.509 Certificate
Signature AlgorithmIdentifier
OID Representation
ASN.1
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3. X.509 Certificate
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4. Algorithms OID
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5. MD5 with RSA
The MD5withRSA OID = 1.2.840.113549.1.1.4
1=>iso
1.2=>iso/memberBody
1.2.840 =>iso/member-body/usa
1.2.840.113549 => iso/memberBody/usa/rsadsi/
1.2.840.113549.1=>iso/memberBody/usa/rsadsi/pkcs
1.2.840.113549.1.1 = >
iso/memberBody/usa/rsadsi/pkcs/pkcs1
1.2.840.113549.1.1.4
=>iso/memberBody/usa/rsadsi/pkcs/pkcs1/MD5
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6. Conversion OID to Hex
1.2.840.113549.1.1.4
2A 86 48 86 F7 0D 01 01 04
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7. Conversion of 840 to 86 48
• Step 1 Convert it into Binary
840 == 1101001000
• Step 2 Longer then 7 bits, break it into seven
or less
1101001000 == 110
1001000
• Step 3 Add higher Order Bits
1101001000 == 10000110 01001000
Or hexadecimal 86 48
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8. Conversion of 113549 to 86 F7 0D
• Step 1 Convert it into Binary
113549 == 11011101110001101
• Step 2 Longer then 7 bits, break it into seven or
less
113549 == 110 1110111 0001101
• Step 3 Make first 2 higher order bits to 1
113549 == 10000110 11110111 00001101
86 F7 0D in hexadecimal
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9. Conversion of 1.2 to 2A
• Algebra :
Z = 40X + Y
Z = 40x1 +2 = 42 =0x2A
Reference : X.690,ASN.1 Encoding Rules
ITU/ISO in ITU X.680 or ISO/IEC 8824
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