Move actual password derivation to separate class

LegacyPasswordGenerator.m

@@ -0,0 +1,51 @@
+#import "LegacyPasswordGenerator.h"
+
+@implementation LegacyPasswordGenerator
+@synthesize length = _length, site = _site, passphrase = _passphrase;
+@synthesize output = _output;
+
++ (instancetype)generator
+{
+	return [[[self alloc] init] autorelease];
+}
+
+- init
+{
+	self = [super init];
+
+	_length = 16;
+
+	return self;
+}
+
+- (void)derivePassword
+{
+	OFSHA256Hash *siteHash = [OFSHA256Hash cryptoHash];
+	[siteHash updateWithBuffer: [_site UTF8String]
+			    length: [_site UTF8StringLength]];
+
+	if (_output != NULL) {
+		of_explicit_memset(_output, 0, _length);
+		[self freeMemory: _output];
+	}
+
+	_output = [self allocMemoryWithSize: _length + 1];
+
+	of_scrypt(8, 524288, 2, [siteHash digest],
+	    [[siteHash class] digestSize], _passphrase, strlen(_passphrase),
+	    _output, _length);
+
+	/*
+	 * This has a bias, however, this is what scrypt-genpass does and the
+	 * legacy mode wants to be compatible to scrypt-genpass.
+	 */
+	_output[0] = "abcdefghijklmnopqrstuvwxyz"[_output[0] % 26];
+	_output[1] = "0123456789"[_output[1] % 10];
+	_output[2] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"[_output[2] % 26];
+
+	for (size_t i = 3; i < _length; i++)
+		_output[i] = "abcdefghijklmnopqrstuvwxyz"
+		    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+		    "0123456789"[_output[i] % (26 + 26 + 10)];
+}
+@end