Problem with gcry_pk_verify

[Jean-Philippe Garcia Ballester]

  I'm using libgcrypt to make a SSH library. So I build a sexp :
gcry_sexp_build(&gcryhash,NULL,"(data(flags pkcs1)(hash sha1 %m))",bn);
where bn is the mpi where the hash is stocked. The problem is that when
the most significant bit is set, the sexp is built like this :
(data 
 (flags pkcs1)
 (hash sha1 #00D5FAD16E753FEEC40B696EC82D1E602A4D5C1302#)
 )
0s are printed because the number is positive, but when gcry_pk_verify gets the mpi, it says the number needs 21 bytes, and is therefore not a valid sha1, failing with GPG_ERR_CONFLICT. How can I solve the problem?
  Regards,

-- 
Jean-Philippe Garcia Ballester
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