これがRC4コードです。とても軽量です。
C は、本番システムで 5 年間使用されています。
軽くテストした Delphi コードを追加しました。Pascal は行単位の移植であり、 with unsigned chargoing to Byte. Delphi自体ではなく、DelphiオプションをオンにしてFree PascalでPascalを実行しただけです。C と Pascal の両方に単純なファイル プロセッサがあります。
暗号文をスクランブルすると、元の平文が返されます。
現在までに報告されたバグはありません。これで問題が解決することを願っています。
rc4.h
#ifndef RC4_H
#define RC4_H
/*
* rc4.h -- Declarations for a simple rc4 encryption/decryption implementation.
* The code was inspired by libtomcrypt. See www.libtomcrypt.org.
*/
typedef struct TRC4State_s {
int x, y;
unsigned char buf[256];
} TRC4State;
/* rc4.c */
void init_rc4(TRC4State *state);
void setup_rc4(TRC4State *state, char *key, int keylen);
unsigned endecrypt_rc4(unsigned char *buf, unsigned len, TRC4State *state);
#endif
rc4.c
void init_rc4(TRC4State *state)
{
int x;
state->x = state->y = 0;
for (x = 0; x < 256; x++)
state->buf[x] = x;
}
void setup_rc4(TRC4State *state, char *key, int keylen)
{
unsigned tmp;
int x, y;
// use only first 256 characters of key
if (keylen > 256)
keylen = 256;
for (x = y = 0; x < 256; x++) {
y = (y + state->buf[x] + key[x % keylen]) & 255;
tmp = state->buf[x];
state->buf[x] = state->buf[y];
state->buf[y] = tmp;
}
state->x = 255;
state->y = y;
}
unsigned endecrypt_rc4(unsigned char *buf, unsigned len, TRC4State *state)
{
int x, y;
unsigned char *s, tmp;
unsigned n;
x = state->x;
y = state->y;
s = state->buf;
n = len;
while (n--) {
x = (x + 1) & 255;
y = (y + s[x]) & 255;
tmp = s[x]; s[x] = s[y]; s[y] = tmp;
tmp = (s[x] + s[y]) & 255;
*buf++ ^= s[tmp];
}
state->x = x;
state->y = y;
return len;
}
int endecrypt_file(FILE *f_in, FILE *f_out, char *key)
{
TRC4State state[1];
unsigned char buf[4096];
size_t n_read, n_written;
init_rc4(state);
setup_rc4(state, key, strlen(key));
do {
n_read = fread(buf, 1, sizeof buf, f_in);
endecrypt_rc4(buf, n_read, state);
n_written = fwrite(buf, 1, n_read, f_out);
} while (n_read == sizeof buf && n_written == n_read);
return (n_written == n_read) ? 0 : 1;
}
int endecrypt_file_at(char *f_in_name, char *f_out_name, char *key)
{
int rtn;
FILE *f_in = fopen(f_in_name, "rb");
if (!f_in) {
return 1;
}
FILE *f_out = fopen(f_out_name, "wb");
if (!f_out) {
close(f_in);
return 2;
}
rtn = endecrypt_file(f_in, f_out, key);
fclose(f_in);
fclose(f_out);
return rtn;
}
#ifdef TEST
// Simple test.
int main(void)
{
char *key = "This is the key!";
endecrypt_file_at("rc4.pas", "rc4-scrambled.c", key);
endecrypt_file_at("rc4-scrambled.c", "rc4-unscrambled.c", key);
return 0;
}
#endif
これは軽くテストされた Pascal です。ソース コードを C でスクランブルし、Pascal 実装で問題なくデスクランブルできます。
type
RC4State = record
x, y : Integer;
buf : array[0..255] of Byte;
end;
KeyString = String[255];
procedure initRC4(var state : RC4State);
var
x : Integer;
begin
state.x := 0;
state.y := 0;
for x := 0 to 255 do
state.buf[x] := Byte(x);
end;
procedure setupRC4(var state : RC4State; var key : KeyString);
var
tmp : Byte;
x, y : Integer;
begin
y := 0;
for x := 0 to 255 do begin
y := (y + state.buf[x] + Integer(key[1 + x mod Length(key)])) and 255;
tmp := state.buf[x];
state.buf[x] := state.buf[y];
state.buf[y] := tmp;
end;
state.x := 255;
state.y := y;
end;
procedure endecryptRC4(var buf : array of Byte; len : Integer; var state : RC4State);
var
x, y, i : Integer;
tmp : Byte;
begin
x := state.x;
y := state.y;
for i := 0 to len - 1 do begin
x := (x + 1) and 255;
y := (y + state.buf[x]) and 255;
tmp := state.buf[x];
state.buf[x] := state.buf[y];
state.buf[y] := tmp;
tmp := (state.buf[x] + state.buf[y]) and 255;
buf[i] := buf[i] xor state.buf[tmp]
end;
state.x := x;
state.y := y;
end;
procedure endecryptFile(var fIn, fOut : File; key : KeyString);
var
nRead, nWritten : Longword;
buf : array[0..4095] of Byte;
state : RC4State;
begin
initRC4(state);
setupRC4(state, key);
repeat
BlockRead(fIN, buf, sizeof(buf), nRead);
endecryptRC4(buf, nRead, state);
BlockWrite(fOut, buf, nRead, nWritten);
until (nRead <> sizeof(buf)) or (nRead <> nWritten);
end;
procedure endecryptFileAt(fInName, fOutName, key : String);
var
fIn, fOut : File;
begin
Assign(fIn, fInName);
Assign(fOut, fOutName);
Reset(fIn, 1);
Rewrite(fOut, 1);
endecryptFile(fIn, fOut, key);
Close(fIn);
Close(fOut);
end;
{$IFDEF TEST}
// Very small test.
const
key = 'This is the key!';
begin
endecryptFileAt('rc4.pas', 'rc4-scrambled.pas', key);
endecryptFileAt('rc4-scrambled.pas', 'rc4-unscrambled.pas', key);
end.
{$ENDIF}