How to write ASN1 encoding in python using PyASN INTEGER (1..MAX)?

Question

I am trying to implement some encoding in Python using PyASN libraries. I have to define a class where I should implement the following :

pbkdf2params ::= SEQUENCE {
salt OCTET STRING,
iterationCount INTEGER (1..MAX),
keyLength INTEGER (1..MAX)
}

And the python class I have defined is as follows:

class pbkdf2params(univ.Sequence):
 componentType = namedtype.NamedTypes(
   namedtype.NamedType('salt', univ.OctetString()),
   namedtype.NamedType('iterationCount', univ.integer(1,MAX)), 
   namedtype.NamedType('keyLength', univ.integer(1, MAX))
   )

But I don't think this is correct especially for integer(1..MAX) . What have I missed? What is the MAX value it takes in this case?

Answer 1

You need to add a value range constraint to Integer object like this:

from pyasn1.type import univ, namedtype, constraint

class Pbkdf2params(univ.Sequence):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType('salt', univ.OctetString()),
        namedtype.NamedType('iterationCount', univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(1,MAX)), 
        namedtype.NamedType('keyLength', univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(1, MAX))
    )

Whenever you attempt to initialize Integer with an out-of-range value, an exception will be thrown.