RC4 PHP decryption fails - php

Question

I have encrypted strings using rc4 encryption. I could decrypt 1st string I have encrypted. But I couldn't successfully decrypt 2nd string onwards. Any idea?
My code
$dpl = 256;
$file = fopen( 'log', "w");
$key = 'sjhdjhd';
$content1 = rc4($key,str_repeat(" ",$dpl).'ABC');
$content1 = substr($content1,$dpl);
$content2 = rc4($key,str_repeat(" ",$dpl).'DEFG');
$content2 = substr($content2,$dpl);
fwrite($file, $content1);
fwrite($file, $content2);
fclose( $file );
$file = fopen( 'log', "r");
while ( $buff = fread( $file, 256 ) ) {
$plaintext = rc4($key,str_repeat(" ",$dpl).$buff);
echo substr($plaintext,$dpl).PHP_EOL;
}
fclose( $file );
function rc4($key, $data)
{
// Store the vectors "S" has calculated
static $SC;
// Function to swaps values of the vector "S"
$swap = create_function('&$v1, &$v2', '
$v1 = $v1 ^ $v2;
$v2 = $v1 ^ $v2;
$v1 = $v1 ^ $v2;
');
$ikey = crc32($key);
if (!isset($SC[$ikey])) {
// Make the vector "S", basead in the key
$S = range(0, 255);
$j = 0;
$n = strlen($key);
for ($i = 0; $i < 255; $i++) {
$char = ord($key{$i % $n});
$j = ($j + $S[$i] + $char) % 256;
$swap($S[$i], $S[$j]);
}
$SC[$ikey] = $S;
} else {
$S = $SC[$ikey];
}
// Crypt/decrypt the data
$n = strlen($data);
$data = str_split($data, 1);
$i = $j = 0;
for ($m = 0; $m < $n; $m++) {
$i = ($i + 1) % 256;
$j = ($j + $S[$i]) % 256;
$swap($S[$i], $S[$j]);
$char = ord($data[$m]);
$char = $S[($S[$i] + $S[$j]) % 256] ^ $char;
$data[$m] = chr($char);
}
return implode('', $data);
}