Some Code pieces to download

• Vigenere ciphers.
  compile with:   cc -o vigenere_solve  vigenere_solve.c -lm
  Run with:    vigenere_solve ciphertextfile

• Extended euclidean Algorithm.
  compile with:    cc  ; -o euclidean  euclidean.c -lm
  Run with:    euclidean  -a12345  -b6789      to get d = gcd(12345,6789).
  Adding the -e option to the command line gives the extended Euclidean Algorithm and adding the -v option gives full step-by-step output.
  Example:    euclidean -a12345 -b6789 -e -v

• Chinese Remainder Theorem. Solves the system of congruences:
      x = a_i (mod n_i)    i = 1, ... k     - assumes gcd(n_i,n_j) = 1    for i not j
  compile with:    cc  -o crt  crt.c
  Run with:  Reads the values a_i and n_i from the command line:
  crt  -a[a₁,a₂,....,a_k]  -n[n₁,n₂,....,n_k]
  The syntax is critical; each value of a and n must be contained within the opening and closing square parenthesis [ ], be separated by a comma and with no spaces.
  Example:     crt  -a[1,2,3]  -n[4,5,6]     solves the congruences
              x = 1 (mod 4),     x = 2 (mod 5),     x = 3 (mod 6)

• Solving linear congruences.
  compile with:    cc  -o solve_congruence  solve_congruence.c
  Run with:    solve_congruence  -a(num)  -b(num)  -n(num)     to get the solution(s) of    a x = b (mod n).
  Example:    solve_congruence  -a5  -b10  -n25     to get solutions x of:    5 x = 10 (mod 25).

• Modular Exponentiations.
  compile with:    cc  -o mod_exp  mod_exp.c
  Run with:    mod_exp  -y(num)  -x(num)  -n(num)     to get    y^x  (mod n).
  Example:    mod_exp  -y123  -x456  -n789     to get    123⁴⁵⁶  (mod 789).

• Calculating the Jacobi symbol.
  compile with:    cc  -o jacobi  jacobi.c
  Run with:    jacobi  -a(num)  -n(num)
  Example:    jacobi  -a123  -n456     to get Jacobi (123/456).

• Calculating continued fractions.
  compile with:    cc  -o cont_frac  cont_frac.c
  Run with:    cont_frac  -x(decimal)  -n(num)     to get the n^th term continued fraction representation to the decimal x.
  Example:    cont_frac  -x3.1415926536  -n4     to get the 4 term continued fraction for π.