Aver lo mas seguro como te dicen... es que tanto el encriptamiento como la comparacion de las contraseñas se hagan en un archivo del lado del servidor como php por ejemplo.
No obstante.... esta es una libreria que hace el encriptamiento md5 con javascript
Código Javascript
:
Ver originalvar hexcase=0;function hex_md5(a){return rstr2hex(rstr_md5(str2rstr_utf8(a)))}function hex_hmac_md5(a,b){return rstr2hex(rstr_hmac_md5(str2rstr_utf8(a),str2rstr_utf8(b)))}function md5_vm_test(){return hex_md5("abc").toLowerCase()=="900150983cd24fb0d6963f7d28e17f72"}function rstr_md5(a){return binl2rstr(binl_md5(rstr2binl(a),a.length*8))}function rstr_hmac_md5(c,f){var e=rstr2binl(c);if(e.length>16){e=binl_md5(e,c.length*8)}var a=Array(16),d=Array(16);for(var b=0;b<16;b++){a[b]=e[b]^909522486;d[b]=e[b]^1549556828}var g=binl_md5(a.concat(rstr2binl(f)),512+f.length*8);return binl2rstr(binl_md5(d.concat(g),512+128))}function rstr2hex(c){try{hexcase}catch(g){hexcase=0}var f=hexcase?"0123456789ABCDEF":"0123456789abcdef";var b="";var a;for(var d=0;d<c.length;d++){a=c.charCodeAt(d);b+=f.charAt((a>>>4)&15)+f.charAt(a&15)}return b}function str2rstr_utf8(c){var b="";var d=-1;var a,e;while(++d<c.length){a=c.charCodeAt(d);e=d+1<c.length?c.charCodeAt(d+1):0;if(55296<=a&&a<=56319&&56320<=e&&e<=57343){a=65536+((a&1023)<<10)+(e&1023);d++}if(a<=127){b+=String.fromCharCode(a)}else{if(a<=2047){b+=String.fromCharCode(192|((a>>>6)&31),128|(a&63))}else{if(a<=65535){b+=String.fromCharCode(224|((a>>>12)&15),128|((a>>>6)&63),128|(a&63))}else{if(a<=2097151){b+=String.fromCharCode(240|((a>>>18)&7),128|((a>>>12)&63),128|((a>>>6)&63),128|(a&63))}}}}}return b}function rstr2binl(b){var a=Array(b.length>>2);for(var c=0;c<a.length;c++){a[c]=0}for(var c=0;c<b.length*8;c+=8){a[c>>5]|=(b.charCodeAt(c/8)&255)<<(c%32)}return a}function binl2rstr(b){var a="";for(var c=0;c<b.length*32;c+=8){a+=String.fromCharCode((b[c>>5]>>>(c%32))&255)}return a}function binl_md5(p,k){p[k>>5]|=128<<((k)%32);p[(((k+64)>>>9)<<4)+14]=k;var o=1732584193;var n=-271733879;var m=-1732584194;var l=271733878;for(var g=0;g<p.length;g+=16){var j=o;var h=n;var f=m;var e=l;o=md5_ff(o,n,m,l,p[g+0],7,-680876936);l=md5_ff(l,o,n,m,p[g+1],12,-389564586);m=md5_ff(m,l,o,n,p[g+2],17,606105819);n=md5_ff(n,m,l,o,p[g+3],22,-1044525330);o=md5_ff(o,n,m,l,p[g+4],7,-176418897);l=md5_ff(l,o,n,m,p[g+5],12,1200080426);m=md5_ff(m,l,o,n,p[g+6],17,-1473231341);n=md5_ff(n,m,l,o,p[g+7],22,-45705983);o=md5_ff(o,n,m,l,p[g+8],7,1770035416);l=md5_ff(l,o,n,m,p[g+9],12,-1958414417);m=md5_ff(m,l,o,n,p[g+10],17,-42063);n=md5_ff(n,m,l,o,p[g+11],22,-1990404162);o=md5_ff(o,n,m,l,p[g+12],7,1804603682);l=md5_ff(l,o,n,m,p[g+13],12,-40341101);m=md5_ff(m,l,o,n,p[g+14],17,-1502002290);n=md5_ff(n,m,l,o,p[g+15],22,1236535329);o=md5_gg(o,n,m,l,p[g+1],5,-165796510);l=md5_gg(l,o,n,m,p[g+6],9,-1069501632);m=md5_gg(m,l,o,n,p[g+11],14,643717713);n=md5_gg(n,m,l,o,p[g+0],20,-373897302);o=md5_gg(o,n,m,l,p[g+5],5,-701558691);l=md5_gg(l,o,n,m,p[g+10],9,38016083);m=md5_gg(m,l,o,n,p[g+15],14,-660478335);n=md5_gg(n,m,l,o,p[g+4],20,-405537848);o=md5_gg(o,n,m,l,p[g+9],5,568446438);l=md5_gg(l,o,n,m,p[g+14],9,-1019803690);m=md5_gg(m,l,o,n,p[g+3],14,-187363961);n=md5_gg(n,m,l,o,p[g+8],20,1163531501);o=md5_gg(o,n,m,l,p[g+13],5,-1444681467);l=md5_gg(l,o,n,m,p[g+2],9,-51403784);m=md5_gg(m,l,o,n,p[g+7],14,1735328473);n=md5_gg(n,m,l,o,p[g+12],20,-1926607734);o=md5_hh(o,n,m,l,p[g+5],4,-378558);l=md5_hh(l,o,n,m,p[g+8],11,-2022574463);m=md5_hh(m,l,o,n,p[g+11],16,1839030562);n=md5_hh(n,m,l,o,p[g+14],23,-35309556);o=md5_hh(o,n,m,l,p[g+1],4,-1530992060);l=md5_hh(l,o,n,m,p[g+4],11,1272893353);m=md5_hh(m,l,o,n,p[g+7],16,-155497632);n=md5_hh(n,m,l,o,p[g+10],23,-1094730640);o=md5_hh(o,n,m,l,p[g+13],4,681279174);l=md5_hh(l,o,n,m,p[g+0],11,-358537222);m=md5_hh(m,l,o,n,p[g+3],16,-722521979);n=md5_hh(n,m,l,o,p[g+6],23,76029189);o=md5_hh(o,n,m,l,p[g+9],4,-640364487);l=md5_hh(l,o,n,m,p[g+12],11,-421815835);m=md5_hh(m,l,o,n,p[g+15],16,530742520);n=md5_hh(n,m,l,o,p[g+2],23,-995338651);o=md5_ii(o,n,m,l,p[g+0],6,-198630844);l=md5_ii(l,o,n,m,p[g+7],10,1126891415);m=md5_ii(m,l,o,n,p[g+14],15,-1416354905);n=md5_ii(n,m,l,o,p[g+5],21,-57434055);o=md5_ii(o,n,m,l,p[g+12],6,1700485571);l=md5_ii(l,o,n,m,p[g+3],10,-1894986606);m=md5_ii(m,l,o,n,p[g+10],15,-1051523);n=md5_ii(n,m,l,o,p[g+1],21,-2054922799);o=md5_ii(o,n,m,l,p[g+8],6,1873313359);l=md5_ii(l,o,n,m,p[g+15],10,-30611744);m=md5_ii(m,l,o,n,p[g+6],15,-1560198380);n=md5_ii(n,m,l,o,p[g+13],21,1309151649);o=md5_ii(o,n,m,l,p[g+4],6,-145523070);l=md5_ii(l,o,n,m,p[g+11],10,-1120210379);m=md5_ii(m,l,o,n,p[g+2],15,718787259);n=md5_ii(n,m,l,o,p[g+9],21,-343485551);o=safe_add(o,j);n=safe_add(n,h);m=safe_add(m,f);l=safe_add(l,e)}return Array(o,n,m,l)}function md5_cmn(h,e,d,c,g,f){return safe_add(bit_rol(safe_add(safe_add(e,h),safe_add(c,f)),g),d)}function md5_ff(g,f,k,j,e,i,h){return md5_cmn((f&k)|((~f)&j),g,f,e,i,h)}function md5_gg(g,f,k,j,e,i,h){return md5_cmn((f&j)|(k&(~j)),g,f,e,i,h)}function md5_hh(g,f,k,j,e,i,h){return md5_cmn(f^k^j,g,f,e,i,h)}function md5_ii(g,f,k,j,e,i,h){return md5_cmn(k^(f|(~j)),g,f,e,i,h)}function safe_add(a,d){var c=(a&65535)+(d&65535);var b=(a>>16)+(d>>16)+(c>>16);return(b<<16)|(c&65535)}function bit_rol(a,b){return(a<<b)|(a>>>(32-b))};
Dale click a "ver original", copias todo el texto a un archivo y lo guardas como md5.js
.