Unformatted text preview: nt to decrypt the message with your private key. Assume you are use the a single pair of public and private key, (Kpub,Kpriv)
Assume
for both encryption/decryption and signing/verification.
Eve, the attacker, records an encrypted letter sent to you by someone else,
and ask you to sign this recorded message (and of course, return the signed
c
result to her). If you follow Eve’s request and sign on what Eve gives you, you
are actually decrypting your own secret letter for Eve.
=> It’s better to use different public/private keypairs for different purposes, e.g.
one keypair (Kpub1, Kpriv1) for letting people to send secret to you by
(Kpub1,
encrypting with Kpub1 and you can decrypt using Kpriv1; use a different pair
Kpub1
Kpriv1 use
(Kpub2,Kpriv2) for digitalsignature/verification, i.e. you use Kpriv2 to sign
(Kpub2,Kpriv2)
outgoing messages and your intended receiptant can use Kpub2 to verify
Kpub2
your signature.
your
Cuberoot attack for e = 3: if m3 < n because the “mod” operation becomes null ,
Cuberoot
i.e. m3 mod n = m3 = C and the attacker can obtain m by performing m = 3 C
i.e.
With e = 3, sending exactly the same secret message to 3 or more people (using
With
3 or more public key) would reveal the secret message ;
3 See http://members.tripod.com/irish_ronan/rsa/attacks.html Public Key Cryptography Standard (PKCS) A llist of Standards (PKCS#1 to PKCS#15) on how to use RSA in
ist
practice, regarding message formatting, information encoding
scheme, choice of parameters etc
Protected against the following “improper use” or attacks on RSA
Protected
including:
including: Plaintext guessing Chosen ciphertext attack m3 < n Sending the same message to multiple people ;
Sending
This is done by prepending some fixed number of constant and
This
random bytes to the message to be encrypted/ decrypted
random Performance of RSA For hardware implementation, RSA is about 1000 times slower
For
than DES ; for software implementation, RSA is about 100 times
slower ;
Time to do RSA decryption on a 1 MIPS VAX was around 30
Time
seconds (VERY SLOW…) when it was invented in late 70’s
seconds
The inventors needed to wo...
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 Fall '13
 CHOWSzeMing,Sherman
 Cryptography, Publickey cryptography

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