CODEWITHSUNDEEP
java-meone-time-password
Garbit
Garbit

Reputation: 6046

OTP S/KEY One Time password - Folding MD5 Digest output

Im trying to create a one time password generator for a phone. In the RFC2289 it specifies that i must fold the output of the MD5, i'm using bouncy castle MD5 and i cant work out how to fold the byte array output. 

for (int i = 0; i < 8; i++)
{
    md5[i] ^= md5[i+8];
}

This is what i have so far

Upvotes: 3

Views: 1046

Answers (1)

C. K. Young
C. K. Young

Reputation: 223153

Probably, you want this:

for (int i = 0; i < 8; ++i)
    md5[i] ^= md5[i + 8];
return Arrays.copyOf(md5, 8);

This way, only the first 64 bits (which are used by OTP) is returned.

Upvotes: 1

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