Sum of digits flaw name request Let's say I am making an encryption algorithm, and in the algorithm in have the following step: "multiply the integer from the previous step by 9 and take the sum of the digits of the resulting number."  By doing this, I've guaranteed that the result will be divisible by 9 in base 10, which let's say I did not expect.  My question is:  What is this error called, if it is an error?  Is this a specific case of a general class of flaws in crypto algorithms?
It depends completely on the algorithm if it would matter that the result would be divisible. If it was a cryptographic error I don't think it would have a specific name. Possibly a side effect or unexpected property.