暗号/フェイステル構造

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    m = "Koreハ平文ﾃﾞｽ♪　 　Koreハ平文ﾃﾞｽ♪ ひゃっはー"
    mes "平文 = 『"+m+"』\n"
    
    mes "フェイステル構造の場合"
    keys = $0ABCDEF0, $FF00FF00, $512, $92843
    c = encrypt_feistel_a(m,keys)
    mes "暗号化文章(Feistel) = 『"+c+"』"
    cc = decrypt_feistel_a(c,keys)
    mes "復号化文章(Feistel) = 『"+cc+"』"
    mes "※本来なら鍵は１本だけで、上手く繁殖させて４本にするらしい"
    mes "round_func_a関数を色々いじくる事で耐久度が上下する\n"
    
 
#module
    #defcfunc encrypt_feistel_a str m, array keys \
    , local mm, local r1, local l1, local c, local index \
    , local key, local l2, local r2
    mm = m
    sdim c, strlen(mm)+8
    r1 = 0
    l1 = 0
    repeat (strlen(mm)+7)/8
        index = cnt*8
        lpoke l1, 0, lpeek(mm,index)
        lpoke r1, 0, lpeek(mm,index+4)
        repeat length(keys)
            l2 = r1
            r2 = (round_func_a(keys(cnt),r1) xor l1)
            l1 = l2
            r1 = r2
        loop
        memcpy c, l1, 4, index
        memcpy c, r1, 4, index+4
    loop
    return c
    
    #defcfunc round_func_a int i1, int i2
    return i1+499*i2+398
    
    #defcfunc decrypt_feistel_a str c, array keys \
    , local cc, local r1, local l1, local m, local index \
    , local key, local l2, local r2
    cc = c
    sdim m, strlen(cc)+8
    r1 = 0
    l1 = 0
    repeat (strlen(cc)+7)/8
        index = cnt*8
        lpoke l1, 0, lpeek(cc,index)
        lpoke r1, 0, lpeek(cc,index+4)
        repeat length(keys)
            key = length(keys)-cnt-1
            r2 = l1
            l2 = (round_func_a(keys(key),l1) xor r1)
            l1 = l2
            r1 = r2
        loop
        memcpy m, l1, 4, index
        memcpy m, r1, 4, index+4
    loop
    return m
#global