Secure Programming

Question 1

How to avoid integer wraparound

Answer 1

BigInt
Try/Catch

Question 2

Python

Answer 2

Python dynamically changes type depending on required space

Question 3

more secure if(==y){…}

Answer 3

tol = 0.001
if abs(x-y)<tol

Question 4

secure symmetric encryption
(LRRS)

Answer 4

Key must be as long as plaintext
key must be random
key must never be reused
key must be kept secret

Question 5

modulus

Answer 5

n=p*q

Question 6

totient φ(n)

Answer 6

φ(n) = (p-1)*(q-1)

Question 7

E

Answer 7

between 1 and φ(n)

e.g.1-12
7

Question 8

D

Answer 8

Modular inverse of E

Question 9

Public-Key

Answer 9

(e,n)

Question 10

Private-Key

Answer 10

(d,n)

Question 11

black box

Answer 11

Simulate attacks externally

Question 12

white box

Answer 12

simulate attacks while knowing the structure

Question 13

sql

Answer 13

declare @inbox int
declare @sql nvarchar(100)

set @inbox = 3; Drop Database
set @sql = ‘select * from review where stars =’ + @stars

Output = select * from reviews; Drop database

Question 14

secure sql

Answer 14

declare @inbox nvarchar(100)
declare @sql nvarchar(100)
declare @param nvarchar(100)
declare @query nvarchar(100)

SET @inbox = ‘3; drop database’;
SET @sql= N’SELECT * FROM REVIEW WHERE stars = @stars’;
SET @paramDefinition = N’@stars NVARCHAR(MAX)’;
SET @query = @SQLstub;

EXEC sp_executesql @SQLQuery, @paramDefinition, @stars = @inbox;

output = SELECT * FROM REVIEW WHERE stars = ‘3; drop database’;

Question 15

RSA encryption (key = (7,12))

Answer 15

Convert string to ASCII
e.g. H = 72
Encryption = C = M^e mod n = C = 72^7 mod 12
Decryptuon = M = C^d mod n = M = C^7 mod 12

Question 16

XOR

Answer 16

ASCII of input XOR with a random bitstring (key)