An example analysis of ENCODE64 encryption algorithm implemented by JavaScript

This JavaScript code can implement the ENCODE64 encryption algorithm, the speed is quite good.

 

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//encode64 codec (function () {var Codechar = " Paawo65gouf7ik2vi9-xq8cftexlcdy1hd3tv0ryzjbpn_blnss4mgrkqwmzjeuh "; window.encode64 = function (str) {var s = ""; var a = strtobytes (str); Gets the byte array of the string, which is twice times the length of the string. var res = a.length% 3; 3 bytes A set of processing, the remaining special processing var i = 2, V; for (; i < a.length i + 3) {//per 3 bytes in 4 characters,//equivalent to 3 characters (actually 6 bytes) encoded in 8 characters (actually 16 bytes)//Looks like a lot of volume expansion, but when compression is enabled, these are offset v = a[i-2] + (A[i-1] << 8) + (A[i] << 16); S + + Codechar.charat (V & 0x3f); S + + Codechar.charat ((v >> 6) & 0x3f); S + + Codechar.charat ((v >>) & 0x3f); S + + Codechar.charat ((v >> 18)); } if (res = = 1) {//Word savings one time, complement 2 characters, 64*64>256 v = a[i-2]; s + + Codechar.charat (V & 0x3f); s + + Codechar.charat (V >> 6) & 0x3f); If else if (res = = 2) {//Word surplus 2 bits, complement 3 bytes, 64*64*64>256*256, so it is feasible v = a[i-2] + (A[i-1] << 8), S + = Codechar. CharAt (v & 0x3f); S + + Codechar.charat ((v >> 6) & 0x3f); S + + Codechar.charat (v >>) & 0x3f); return s; }; Window.decode64 = function (codestr) {var dic = []; for (var i = 0; i < codechar.length; i++) {Dic[codechar.charat (i)] = i; var code = []; var res = codestr.length% 4; var i = 3, V; for (; i < codestr.length i + 4) {v = Dic[codestr.charat (i-3)]; v = = Dic[codestr.charat (i-2)] << 6; v + = d Ic[codestr.charat (i-1)] << 12; V + + Dic[codestr.charat (i)] << 18; Code.push (V & 0xFF, (v >> 8) & 0xFF, (v >>) & 0xff); } if (res = = 2) {//The correct number of bytes is definitely 2 or 3, there is no 1 case, if present, discard. V = Dic[codestr.charat (i-3)]; v + + Dic[codestr.charat (i-2)] <& Lt 6; Code.push (v & 0xff); else if (res = = 3) {v = Dic[codestr.charat (i-3)]; v + + Dic[codestr.charat (i-2)] << 6 V + = Dic[codestr.charat (i-1)] << 12; Code.push (V & 0xFF, (v >> 8) & 0xff); return strfrombytes (code); }; })();