秋數(shù)學(xué)實(shí)驗(yàn)實(shí)驗(yàn)報(bào)告4密碼學(xué)初步

1、1 編一個(gè)函數(shù)統(tǒng)計(jì)一段英文文章中各字母出現(xiàn)的頻率。返回值是一個(gè)元胞數(shù)組，第二個(gè)值是文章中按A到Z的順序各個(gè)字母出現(xiàn)的頻率。function y = myStat()ch = textread(,'%c');y=; total = 0;y1 = char(65:90);freq = zeros(1, 26);n = numel(ch);for i = 1:n for j = 0:25 if (ch(i) = j + 65 | ch(i) = j + 97) freq(j+1) = freq(j+1) + 1; total = total + 1; end endendy2= fr

2、eq/total;2 編一個(gè)函數(shù)，在已知密鑰的情況下，用加法密碼進(jìn)行加密和解密。加密算法：function y = encrypt(origin, key)n = numel(origin);for i = 1:n if (origin(i) >= 'A' && origin(i) <= 'Z') origin(i) = rem(26 + origin(i) + key - 'A', 26) + 'A' elseif (origin(i) >= 'a' && ori

3、gin(i) <= 'z') origin(i) = rem(26 + origin(i) + key - 'a', 26) + 'a' endendy = origin;解密算法:function y = decrypt(cryptograph, key)n = numel(cryptograph);for i = 1:n if (cryptograph(i) >= 'A' && cryptograph(i) <= 'Z') cryptograph(i) = rem(26 + c

4、ryptograph(i) - key - 'A', 26) + 'A' elseif (cryptograph(i) >= 'a' && cryptograph(i) <= 'z') cryptograph(i) = rem(26 + cryptograph(i) - key - 'a', 26) + 'a' endendy = cryptograph;3編一個(gè)函數(shù)，在已知密鑰的情況下，對(duì)維吉尼亞密碼進(jìn)行加密和解密。加密函數(shù)：function y = encrypt(o

5、rigin, key)n = numel(origin);m = numel(key);for i = 1:n if (origin(i) >= 'A' && origin(i) <= 'Z') index = rem(i, m); if (index) index = m; end origin(i) = rem(26 + origin(i) + MyOffset(key(index) - 'A', 26) + 'A' elseif (origin(i) >= 'a' &

6、& origin(i) <= 'z') index = rem(i, m); if (index) index = m; end origin(i) = rem(26 + origin(i) + MyOffset(key(index) - 'a', 26) + 'a' endendy = origin;解密函數(shù)：function y = decrypt(cryptograph, key)n = numel(cryptograph);m = numel(key);for i = 1:n if (cryptograph(i) >=

7、 'A' && cryptograph(i) <= 'Z') index = rem(i, m); if (index) index = m; end cryptograph(i) = rem(26 + cryptograph(i) - MyOffset(key(index) - 'A', 26) + 'A' elseif (cryptograph(i) >= 'a' && cryptograph(i) <= 'z') index = rem(i, m); if (index) index = m; end cryptograph(i) = rem(26 + cryptograph(i) - MyOffset(key(index) - 'a', 26) + 'a' endendy = cryptograph;輔助函數(shù)：function y = MyOffset(x)if (x >= 'A' && x <= 'Z') y = x - 'A'els