law: Transfer of Property Act, 1882
  59. Mortgage when to be by assurance
  Where the principal money secured is one hundred rupees or
  
  upwards, a mortgage other than a mortgage by deposit of title deeds can be
  
  effected only by a registered instrument signed by the mortgagor and attested
  
  by at least two witnesses.
  Where the principal money secured is less than one hundred
  
  rupees, a mortgage may be effected either by a registered instrument signed and
  
  attested as aforesaid or (except in the case of a simple mortgage) by delivery
  
  of the property.