Tài liệu hướng dẫn thực hành

Written by Thong D. Nguyen Thursday, 16 September 2010 10:37

Courses - Cryptography

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Tài liệu hướng dẫn thực hành môn "Nhập môn lý thuyết mã hoá thông tin".

Ngôn ngữ: Python

Nội dung: gồm 6 chương:

1. Tổng quan về Python (yêu cầu tự đọc)
2. Mật mã cổ điển
3. Mã đối xứng hiện đại và mã công khai
4. Hàm băm mật mã
5. Hệ mã logarit rời rạc
6. Chữ ký điện tử

Comments  

 

+1 # Thong D. Nguyen 2010-10-07 06:32

Code:def cesar(p,k):
abc='ABCDEFGHIJKLMNOPQRSTUVWXYZ';
c='';
for j in range(len(p)):
c += abc[(abc.index(p[j])+k)%len(abc)];
return c;

Mã Cesar

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0 # Thong D. Nguyen 2010-10-07 06:45

Code:def cesar2(p,k):
k_cur = k;
c = p;
while k_cur > 0:
c = cesar(c, k_cur % 10);
k_cur /= 10;
return c;

Mã Cesar 2

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0 # Thong D. Nguyen 2010-10-07 09:56

Code:def cesar2_d(c,k):
k_cur = int(str(k)[::-1]);
p = c;
while k_cur > 0:
p = cesar_d(p, k_cur % 10);
k_cur /= 10;
return p;

Mã Cesar 2 Decode

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0 # Thong D. Nguyen 2010-10-07 09:38

Code:def cesar_d(c,k):
abc='ABCDEFGHIJKLMNOPQRSTUVWXYZ';
p='';
for i in range(len(c)):
p += abc[(abc.index(c)-k)%len(abc)];
return p;

Cesar Decode

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0 # Thong D. Nguyen 2010-10-07 06:59

Code:k='DLRYVOHEZXWPTBGFJQNMUSKACI';

def subs(p,k):
abc='ABCDEFGHIJKLMNOPQRSTUVWXYZ';
if len(abc) != len(k):
return '';
c='';
for j in range(len(p)):
c += k[abc.index(p[j])];
return c;

Mã thay thế

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0 # Thong D. Nguyen 2010-10-07 10:21

Code:def subs_d(c,k):
abc='ABCDEFGHIJKLMNOPQRSTUVWXYZ';
if len(abc) != len(k):
return '';
p='';
for j in range(len(c)):
p += abc[k.index(c[j])];
return p;

Mã thay thế (Decode)

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0 # Thong D. Nguyen 2010-10-07 07:51

Code:def affine(p,k):
abc='ABCDEFGHIJKLMNOPQRSTUVWXYZ';
a=k[0];
b=k[1];
c='';
for i in range(len(p)):
x = abc.index(p);
c += abc[(a*x+b)%len(abc)];
return c;

Mã Affine

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0 # Thong D. Nguyen 2010-10-07 09:12

Code:def affine6(p,k):
return affine(cesar(cesar(p, k[1]), k[0]), k);

Mã Affine 6

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0 # Thong D. Nguyen 2010-10-07 09:20

Code:def affine7(p,k):
abc='ABCDEFGHIJKLMNOPQRSTUVWXYZ';
c = '';
for j in range(len(p)):
ki = [k[0], abc.index(cesar(p[j], k[1]))];
c += affine(p[j], k);
return c;

Mã Affine 7

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0 # Thong D. Nguyen 2010-10-08 07:50

Code:def egcd(a, b):
"""Returns a triple (g, x, y), such that ax + by = g = gcd(a,b). Assumes a, b >= 0."""
if a == 0:
return (b, 0, 1)
else:
g, y, x = egcd(b % a, a)
return (g, x - (b // a) * y, y)

def modinv(a, m):
g, x, y = egcd(a, m)
if g != 1:
return None
else:
return x % m


Modular inverse
Source: www.algorithmist.com/index.php/Modular_inverse

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