rsa ns2

rsa ns2 – RSA is a cryptosystem for public-key encryption, and is widely used for securing sensitive data, particularly when being also sent over an insecure network.

What is rsa?

• Ron Rivest, Adi Shamir, and also Leonard Adleman introduce a cryptographic algorithm.
• The RSA-algorithm is also based on the fact that there is no efficient way to factor very large numbers. Deducing an RSA-key, also therefore, requires an extraordinary amount of computer processing power and time.

Sample RSA NS2 Code

     proc rsa_encrypt {
input skey
} {
         upvar $skey key
 
        if {
[bitsize $key(n)] < [bitsize $input]
} {
             error "keysize [bitsize $key(n)] must be greater than text [bitsize $input]/$input"
         }
        return [powm $input $key(e) $key(n)]
     }
 
proc rsa_decrypt {
input skey
} {         upvar $skey key
         if {
[bitsize $key(n)] < [bitsize $input]
} {
 
            error "keysize [bitsize $key(n)] must be greater than text [bitsize $input]/$input"
  }
         if {
!

} {
             return [rsa_slow_decrypt $input key]
 }
         set m1 [powm $input [fdiv_r $key(d) [sub_ui $key(p) 1]] $key(p)]
        set m2 [powm $input [fdiv_r $key(d) [sub_ui $key(q) 1]] $key(q)]
        set h [sub $m2 $m1]
        if {
[cmp_si $h 0] < 0
} {
             set h [add $h $key(q)]
 }
        set h [fdiv_r [mul $key(u) $h] $key(q)]
        set m [add $m1 [mul $h $key(p)]]
         return $m
     }
    proc rsa_slow_decrypt {
input pkey
} {
         upvar $pkey key
         if {
[bitsize $key(n)] < [bitsize $input]
} {
             error "keysize [bitsize $key(n)] must be greater than text [bitsize $input]/$input"
         }
        if {
[catch {
set ptext [powm $input $key(d) $key(n)]
}]
} {
             puts "rsa_slow_decrypt: $input [hex $key(d)] [hex $key(n)]"
            error "powm error"
         }
        return $ptext
   }
         proc pack_text {
ptext keylen
} {
        while {
[string length $ptext] < ($keylen - 16)
} {
             append ptext [binary format H* [::md5::md5 $ptext]]
         }
         if {
[string length $ptext] < $keylen
} {
             set md5 [binary format H* [::md5::md5 $ptext]]
            append ptext [string range $md5 0 [expr $keylen - [string length $ptext] - 1]]
         }
         binary scan $ptext H* hex
        return [convert 0x$hex]
  }
     proc encrypt {
ptext pkey
} {
         upvar $pkey key
         set keylen [bytesize $key(n)]
         set en [pack_text $ptext $keylen]
        set en [rsa_encrypt $en key]
        append ctext [hex $en]
         set ctext [binary format H* $ctext]
        return $ctext
  }