[jira] Updated: (DIRTSEC-4) Offset value set to 0 when extracting DBC from hmac-sha1 output

["javier tellez (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DIRTSEC-4?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

javier tellez updated DIRTSEC-4:
--------------------------------

    Attachment: DIRTSEC-4-1.patch

First byte of binary (Binary Dynamic Code) should point to byte hash[19]&0x0f

 triplesec/otp/src/main/java/org/safehaus/otp/Hotp.java


> Offset value set to 0 when extracting DBC from hmac-sha1 output
> ---------------------------------------------------------------
>
>                 Key: DIRTSEC-4
>                 URL: https://issues.apache.org/jira/browse/DIRTSEC-4
>             Project: Triplesec
>          Issue Type: Bug
>         Environment: JavaME mobile phone platform and validation server.
>            Reporter: javier tellez
>         Attachments: DIRTSEC-4-1.patch
>
>
> Hotp.java class implements RFC4226 "HOTP: An HMAC-Based One-Time Password Algorithm".
> In that class,
>    hotp.generate(secret, counter, digits) uses 
>    int offset = 0; 
> Section 5.4 from RFC
> "The following code example describes the extraction of a dynamic
> binary code given that hmac_result is a byte array with the HMACSHA-1 result:
>    int offset = hmac_result[19] & 0xf ;
>    int bin_code = (hmac_result[offset] & 0x7f) << 24
>                         | (hmac_result[offset+1] & 0xff) << 16
>                         | (hmac_result[offset+2] & 0xff) << 8
>                         | (hmac_result[offset+3] & 0xff)
> "
> that is, the offset is the least significant nibble from the last byte of 
> hotp.stepOne() output (the 20 bytes from hmac-sha1(k,c))
> Solved by setting offset to this value
> int offset = hmac_result[19] & 0xf; 

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