Long username length in SIP digest authentication hash

Hi,

Using

-m 11400 = SIP digest authentication (MD5)

with Hash format:

$sip$*uri_server*uri_client*user*realm*method*uri_prefix*uri_resource*uri_suffix​/md5(entityBody)*nonce*nonce_client*nonce_count*qop*directive*md5hash


I get a salt-Length exception when "user" length is longer than 12 char. In my case it has 31 char...

How could i solve it?

Thank you