PHP encryption methods and principles

I am interested in studying the encryption methods and principles of PHP. I can't say that I can't encrypt it. I just used URL encoding and BASE64 encoding for conversion. The code is as follows:

// Differentiate the numbers 0 and the characters O"
$ OOO000000 = urldecode ('% 66% 67% 36% 73% 62% 65% 68% 70% 72% 61% 34% 63% 6f % 5f % 74% 6e % 64 ');
// Decodes the encoded URL string. the decoded result is fg6sbehpra4co_tnd.
$ Ooo=o0 = $ ooo=00 {4}. $ ooo=00 {9}. $ ooo=00 {3}. $ ooo=00 {5 };
// Obtain the decoded characters 4, 9, 3, and 5 and connect them together. The result is base.
// Similarly, the final result is base64_decode.
$ Ooo=o0. = $ ooo=00 {2}. $ ooo=00 {10}. $ ooo=00 {13}. $ ooo=00 {16 };
$ Ooo=o0. = $ ooo=o0 {3}. $ ooo=00 {11}. $ ooo=00 {12}. $ ooo=o0 {7}. $ ooo=00 {5 };
?>

The code is as follows:

// $ GLOBALS defined variable. The value of $ GLOBALS ['ooo=o0'] is base64_decode. then, it is used to decode the subsequent string and the result is $ IIIIIIIIIIII = 'header '; $ IIIIIIIIIl11 = 'is _ file'; eval executes the parsed string and obtains the corresponding variable.
?>

The code is as follows:

$ OOO000O00 = $ OOO000000 {0}. $ OOO000000 {12}. $ OOO000000 {7}. $ OOO000000 {5}. $ OOO000000 {15 };
// Same as above, $ OOO000O00 = 'fopen' is available'
$ O0O000O00 = $ OOO000000 {0}. $ OOO000000 {1}. $ OOO000000 {5}. $ OOO000000 {14 };
// $ O0O000O00 = 'fget'
$ O0O000O0O = $ O0O000O00. $ OOO000000 {11 };
// $ O0O000O0O = 'fgetc'
$ O0O000O00 = $ O0O000O00. $ OOO000000 {3 };
// $ O0O000O00 = 'fgets'
$ O0O00OO00 = $ OOO000000 {0}. $ OOO000000 {8}. $ OOO000000 {5}. $ OOO000000 {9}. $ OOO000000 {16 };
// $ O0O00OO00 = 'fread'
$ OOO00000O = $ OOO000000 {3}. $ OOO000000 {14}. $ OOO000000 {8}. $ OOO000000 {14}. $ OOO000000 {8 };
// $ OOO00000O = 'strtr'
$ OOO0O0O00 =__ FILE __;
// Obtain the current file path and file name
$ OO00O0000 = 0x100;

Eval ($ ooo1_o0 ('invalid bytes = '));
/* The result is
$ Region = $ OOO000O00 ($ region, 'RB'); $ O0O00OO00 ($ O000O0O00, 0x526); $ region = $ ooo1_o0 ($ OOO00000O ($ O0O00OO00 ($ region, 0x17c), 'Maid ($ OO00O00O0 );

Restored and equivalent replacement are available.
$ Fp = fopen (_ FILE __, 'RB ');
Fread ($ fp, 0x526 );
$ Buf = fread ($ fp, 0x17c );
$ Str = base64_decode (strtr ($ buf, 'zbxlbfmc62lpckxpadrguh94k7qns5vvrwzyi/gO0ATYMDqtofEIu + he3366j18ns = ', 'samples + /'));
Eval ($ str );
*/
Return;?> Eu ~ FQ \ FRCgGpG @ Lo' samples + records + 8mrUfF4 + records + WaK9dEd + H6XGdpk + FXUIH95/24VO/aph51_fu9u + records + XG + BdU/kuh1_49f/records + Records/5 records = xzd2rU/2rU/2rU/hybrid + MOrU/2rU/2rU/2NLbf2 + hybrid/g6xRirU/2rU/2rU/hybrid/2rU/2rU/2rU/2rU/2rr55lx2cNhkW5m/hybrid/2rU/ 2rU/2rUiO4rRzGm8yK4dANh3w6m/qSedWNmozlGD8xR = kLHgJcZ [ZM