diff --git a/main.f90 b/main.f90
new file mode 100644
index 0000000..2d4bb3d
--- /dev/null
+++ b/main.f90
@@ -0,0 +1,229 @@
+! FortranでRSA暗号を作る(C++からの書き換え)
+module rsa
+    implicit none
+    type rsa_class
+        integer(8) p, q, n, l, e, d, m
+    end type
+
+    interface operator(.nxor.)
+        module procedure nxor
+    end interface
+
+    interface operator(.lsh.)
+        module procedure l_shift
+    end interface
+
+    interface operator(.rsh.)
+        module procedure r_shift
+    end interface
+contains
+    integer(8) function random(w)
+        implicit none
+        integer(8), intent(inout) :: w
+        integer(8), save :: x = 123456789, y = 362436069, z = 521288629
+        integer(8) t
+        t = x .nxor. (x .lsh. 11_8)
+        x = y; y = z; z = w
+        w = (w .nxor. (w .rsh. 19_8)) .nxor. (t .nxor. (t .rsh. 8_8))
+        random = w 
+    end function random
+
+    ! エラトステネスの篩を使ったやつ
+    subroutine init(rc)
+        implicit none
+        logical(8), allocatable :: sieve(:)
+        integer(8) :: MAX = 8000000
+        integer(8) tmp, t, i, j
+        type(rsa_class), intent(inout) :: rc
+        allocate(sieve(MAX))
+        sieve(:) = .true.
+        sieve(1) = .false.
+        do i = 3, MAX, 2
+            if (sieve(i)) then
+                do j = i * 2, MAX, i
+                    sieve(j) = .false.
+                end do
+            end if
+        end do
+        t = time()
+        tmp = mod(random(t), MAX) + 1
+        do
+            if (sieve(tmp)) then
+                rc%q = tmp
+                exit
+            end if
+            tmp = tmp + 1
+        end do
+        tmp = mod(random(t), MAX) + 1
+        do
+            if (sieve(tmp)) then
+                rc%p = tmp
+                exit
+            end if
+            tmp = tmp + 1
+        end do
+        if (rc%p < rc%q) then
+            tmp  = rc%p
+            rc%p = rc%q
+            rc%q = tmp
+        end if
+        deallocate(sieve)
+    end subroutine init
+
+    integer(8) function nxor(a, b) result(c)
+        implicit none
+        integer(8), intent(in) :: a, b
+        c = xor(a, b)
+    end function nxor
+
+    integer(8) function l_shift(a, b) result(c)
+        implicit none
+        integer(8), intent(in) :: a, b
+        c = lshift(a, b)
+    end function l_shift
+
+    integer(8) function r_shift(a, b) result(c)
+        implicit none
+        integer(8), intent(in) :: a, b
+        c = rshift(a, b)
+    end function r_shift
+end module rsa
+
+program main
+    use rsa
+    implicit none
+    integer(8) plain_num, encrypted_num
+    type(rsa_class) :: rc
+    call init(rc)
+    rc%n = rc%p * rc%q
+    rc%l = lcm(rc%p - 1, rc%q - 1)
+    rc%e = 65537
+    do while (gcd(rc%l, rc%e) .ne. 1)
+        rc%e = rc%e + 1
+    end do
+    rc%d = extended_euclidean(rc%l, rc%e)
+    do while (mod((rc%e * rc%d), rc%l) .ne. 1)
+        rc%d = rc%d + 1
+    end do
+    print '("P : ", I0, "  Q : ", I0)', rc%p, rc%q
+    print '("N : ", I0, "  L : ", I0, "  E : ", I0, "  D : ", I0)', rc%n, rc%l, rc%e, rc%d
+    write (*, '(A)', advance='no') "plain_num     : "
+    read *, plain_num
+    encrypted_num = modPow(plain_num, rc%e, rc%n)
+    print '("encrypted_num : ", I0)', encrypted_num
+    rc%m = Chinese_Remainder_Theorem(rc%p, rc%q, encrypted_num, rc%d)
+    print '("decrypted_num : ", I0)', rc%m
+    read *
+contains
+    ! 最大公約数
+    pure integer(8) function gcd(a, b)
+        implicit none
+        integer(8), intent(in) :: a, b
+        integer(8) r, x, y
+        if (a .eq. 0) gcd = b
+        if (b .eq. 0) gcd = a
+        x = a
+        y = b
+        do
+            r = mod(x, y)
+            if (r .eq. 0) exit
+            x = y
+            y = r
+        end do
+        gcd = y
+    end function gcd
+
+    ! 最小公倍数
+    pure integer(8) function Lcm(x, y)
+        implicit none
+        integer(8), intent(in) :: x, y
+        Lcm = x / gcd(x, y) * y
+    end function Lcm
+
+    ! 拡張ユークリッドの互除法
+    pure integer(8) function extended_euclidean(a, b)
+        implicit none
+        integer(8), intent(in) :: a, b
+        integer(8) s, t, xs, ys, xt, yt
+        integer(8) tmp, u, xu, yu
+        s  = a
+        t  = b
+        xs = 1
+        ys = 0
+        xt = 0
+        yt = 1
+        do while (mod(s, t) .ne. 0)
+            tmp = s / t
+            u   = s - t * tmp
+            xu  = xs - xt * tmp
+            yu  = ys - yt * tmp
+            s   = t
+            xs  = xt
+            ys  = yt
+            t   = u
+            xt  = xu
+            yt  = yu
+        end do
+        if (xt > yt) then
+            extended_euclidean = xt
+        else
+            extended_euclidean = yt
+        end if
+    end function extended_euclidean
+
+    ! べき剰余
+    pure integer(8) function modPow(a, k, n)
+        implicit none
+        integer(8), intent(in) :: a, k, n
+        integer(8) i, va, t
+        t = mod(a, n)
+        if (a .eq. 0 .or. n .eq. 0) then
+            modPow = 0
+        else if (k .eq. 0) then
+            modPow = mod(1, n)
+        end if
+        va = 1
+        do i = 0, k-1
+            va = va * t
+            if (va >= n) va = mod(va, n)
+        end do
+        modPow = va
+    end function modPow
+
+    ! モジュラ逆元
+    pure integer(8) function modinv(a, m)
+        implicit none
+        integer(8), intent(in) :: a, m
+        integer(8) j, i, b, c, x, y
+        b = m
+        c = a
+        j = 1
+        i = 0
+        do while (c .ne. 0)
+            x = b / c
+            y = b - x*c
+            b = c
+            c = y
+            y = j
+            j = i - j*x
+            i = y
+        end do
+        if (i < 0) i = i + m
+        modinv = i
+    end function modinv
+
+    ! 中国剰余定理
+    pure integer(8) function Chinese_Remainder_Theorem(p, q, c, d)
+        implicit none
+        integer(8), intent(in) :: p, q, c, d
+        integer(8) m1, m2, dp, dq, qinv, m, h
+        qinv = modinv(q, p)
+        dp   = mod(d, (p-1))
+        dq   = mod(d, (q-1))
+        m1   = modPow(c, dp, p)
+        m2   = modPow(c, dq, q)
+        h    = qinv * (m1 - m2)
+        m    = m2 + h * q
+        Chinese_Remainder_Theorem = m
+    end function Chinese_Remainder_Theorem
+end program main