Display a random string in a html form

There are a lot of answers to this question, but none of them leverage a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG).

The simple, secure, and correct answer is to use RandomLib and don't reinvent the wheel.

With a secure integer generator in place, generating a random string with a CSPRNG is a walk in the park.

function random_str($length, $keyspace = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
{
    $str = '';
    $max = mb_strlen($keyspace, '8bit') - 1;
    for ($i = 0; $i < $length; ++$i) {
        $str .= $keyspace[random_int(0, $max)];
    }
    return $str;
}


<form name="name" method="post" action="sendform.php">
    <table width="450px">
        <tr>
            <td valign="top">
                <label for="number">Number</label>
            </td>
            <td valign="top">
                <input  type="text" value="<?php echo random_str(10); ?>" maxlength="50" size="30">
            </td>
        </tr>
    </table>
</form>

Try this..

<?php $rand = substr(str_shuffle("abcdefghijklmnopqrstuvwxyz"), 0, 7); ?>
.
.
.
<td valign="top">
<input  type="text" value="<?php echo $rand; ?>" maxlength="50" size="30">
</td>

You can Refer this answer by Roko C. Buljan

function randNumber(len, an){
    an = an&&an.toLowerCase();
    var str="", i=0, min=an=="a"?10:0, max=an=="n"?10:62;
    for(;i++<len;){
      var r = Math.random()*(max-min)+min <<0;
      str += String.fromCharCode(r+=r>9?r<36?55:61:48);
    }
    return str;
}
document.getElementById("foo").value = randNumber(10,'A');

<textarea id='foo' style='width:100%;height:200px'></textarea>

function for making sh1 hash

function sha1 ( str ) { 

var rotate_left = function(n,s) {
        var t4 = ( n<<s ) | (n>>>(32-s));
        return t4;
    };

var lsb_hex = function(val) {
        var str="";
        var i;
        var vh;
        var vl;

        for( i=0; i<=6; i+=2 ) {
            vh = (val>>>(i*4+4))&0x0f;
            vl = (val>>>(i*4))&0x0f;
            str += vh.toString(16) + vl.toString(16);
        }
        return str;
    };

var cvt_hex = function(val) {
        var str="";
        var i;
        var v;

        for( i=7; i>=0; i-- ) {
            v = (val>>>(i*4))&0x0f;
            str += v.toString(16);
        }
        return str;
    };

var blockstart;
var i, j;
var W = new Array(80);
var H0 = 0x67452301;
var H1 = 0xEFCDAB89;
var H2 = 0x98BADCFE;
var H3 = 0x10325476;
var H4 = 0xC3D2E1F0;
var A, B, C, D, E;
var temp;

str = this.utf8_encode(str);
var str_len = str.length;

var word_array = new Array();
for( i=0; i<str_len-3; i+=4 ) {
    j = str.charCodeAt(i)<<24 | str.charCodeAt(i+1)<<16 |
    str.charCodeAt(i+2)<<8 | str.charCodeAt(i+3);
    word_array.push( j );
}

switch( str_len % 4 ) {
    case 0:
        i = 0x080000000;
    break;
    case 1:
        i = str.charCodeAt(str_len-1)<<24 | 0x0800000;
    break;
    case 2:
        i = str.charCodeAt(str_len-2)<<24 | str.charCodeAt(str_len-1)<<16 | 0x08000;
    break;
    case 3:
        i = str.charCodeAt(str_len-3)<<24 | str.charCodeAt(str_len-2)<<16 | str.charCodeAt(str_len-1)<<8    | 0x80;
    break;
}

word_array.push( i );

while( (word_array.length % 16) != 14 ) word_array.push( 0 );

word_array.push( str_len>>>29 );
word_array.push( (str_len<<3)&0x0ffffffff );

for ( blockstart=0; blockstart<word_array.length; blockstart+=16 ) {
    for( i=0; i<16; i++ ) W[i] = word_array[blockstart+i];
    for( i=16; i<=79; i++ ) W[i] = rotate_left(W[i-3] ^ W[i-8] ^ W[i-14] ^ W[i-16], 1);

    A = H0;
    B = H1;
    C = H2;
    D = H3;
    E = H4;

    for( i= 0; i<=19; i++ ) {
        temp = (rotate_left(A,5) + ((B&C) | (~B&D)) + E + W[i] + 0x5A827999) & 0x0ffffffff;
        E = D;
        D = C;
        C = rotate_left(B,30);
        B = A;
        A = temp;
    }

    for( i=20; i<=39; i++ ) {
        temp = (rotate_left(A,5) + (B ^ C ^ D) + E + W[i] + 0x6ED9EBA1) & 0x0ffffffff;
        E = D;
        D = C;
        C = rotate_left(B,30);
        B = A;
        A = temp;
    }

    for( i=40; i<=59; i++ ) {
        temp = (rotate_left(A,5) + ((B&C) | (B&D) | (C&D)) + E + W[i] + 0x8F1BBCDC) & 0x0ffffffff;
        E = D;
        D = C;
        C = rotate_left(B,30);
        B = A;
        A = temp;
    }

    for( i=60; i<=79; i++ ) {
        temp = (rotate_left(A,5) + (B ^ C ^ D) + E + W[i] + 0xCA62C1D6) & 0x0ffffffff;
        E = D;
        D = C;
        C = rotate_left(B,30);
        B = A;
        A = temp;
    }

    H0 = (H0 + A) & 0x0ffffffff;
    H1 = (H1 + B) & 0x0ffffffff;
    H2 = (H2 + C) & 0x0ffffffff;
    H3 = (H3 + D) & 0x0ffffffff;
    H4 = (H4 + E) & 0x0ffffffff;
}

var temp = cvt_hex(H0) + cvt_hex(H1) + cvt_hex(H2) + cvt_hex(H3) + cvt_hex(H4);
return temp.toLowerCase();

}