Lot a time its being needed that we have to encrypt the data before we transmit over air, for this iOS also provides support for encoding and decoding the string or data we want to transmit or receive into a an encrypted format. Most common mode for encoding as I know is Base64, it similar to other coding except all the bits are converted to Number system having base as 64(Just as Binary is base 2, octal is base 8).
iOS itself provides very useful and efficient methods to convert between Base64 and other encodings. I have just tried to give a model class which will simply allow user to call the methods and get the desired output.
This code snippet is for Encoding normal NSData or NSString into Base64 NSString or NSData
#import "Base64.h"
#import
#if !__has_feature(objc_arc)
#error This library requires automatic reference counting
#endif
@implementation NSData (Base64)
+ (NSData *)dataWithBase64EncodedString:(NSString *)string
{
const char lookup[] =
{
99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 62, 99, 99, 99, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 99, 99, 99, 99, 99, 99,
99, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 99, 99, 99, 99, 99,
99, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 99, 99, 99, 99, 99
};
NSData *inputData = [string dataUsingEncoding:NSASCIIStringEncodingallowLossyConversion:YES];
long long inputLength = [inputData length];
const unsigned char *inputBytes = [inputData bytes];
long long maxOutputLength = (inputLength / 4 + 1) * 3;
NSMutableData *outputData = [NSMutableData dataWithLength:maxOutputLength];
unsigned char *outputBytes = (unsigned char *)[outputData mutableBytes];
int accumulator = 0;
long long outputLength = 0;
unsigned char accumulated[] = {0, 0, 0, 0};
for (long long i = 0; i < inputLength; i++)
{
unsigned char decoded = lookup[inputBytes[i] & 0x7F];
if (decoded != 99)
{
accumulated[accumulator] = decoded;
if (accumulator == 3)
{
outputBytes[outputLength++] = (accumulated[0] << 2) | (accumulated[1] >> 4);
outputBytes[outputLength++] = (accumulated[1] << 4) | (accumulated[2] >> 2);
outputBytes[outputLength++] = (accumulated[2] << 6) | accumulated[3];
}
accumulator = (accumulator + 1) % 4;
}
}
//handle left-over data
if (accumulator > 0) outputBytes[outputLength] = (accumulated[0] << 2) | (accumulated[1] >> 4);
if (accumulator > 1) outputBytes[++outputLength] = (accumulated[1] << 4) | (accumulated[2] >> 2);
if (accumulator > 2) outputLength++;
//truncate data to match actual output length
outputData.length = outputLength;
return outputLength? outputData: nil;
}
- (NSString *)base64EncodedStringWithWrapWidth:(NSUInteger)wrapWidth
{
//ensure wrapWidth is a multiple of 4
wrapWidth = (wrapWidth / 4) * 4;
constchar lookup[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
long long inputLength = [self length];
const unsigned char *inputBytes = [self bytes];
long long maxOutputLength = (inputLength / 3 + 1) * 4;
maxOutputLength += wrapWidth? (maxOutputLength / wrapWidth) * 2: 0;
unsigned char *outputBytes = (unsigned char *)malloc(maxOutputLength);
long long i;
long long outputLength = 0;
for (i = 0; i < inputLength - 2; i += 3)
{
outputBytes[outputLength++] = lookup[(inputBytes[i] & 0xFC) >> 2];
outputBytes[outputLength++] = lookup[((inputBytes[i] & 0x03) << 4) | ((inputBytes[i + 1] & 0xF0) >> 4)];
outputBytes[outputLength++] = lookup[((inputBytes[i + 1] & 0x0F) << 2) | ((inputBytes[i + 2] & 0xC0) >> 6)];
outputBytes[outputLength++] = lookup[inputBytes[i + 2] & 0x3F];
//add line break
if (wrapWidth && (outputLength + 2) % (wrapWidth + 2) == 0)
{
outputBytes[outputLength++] = '\r';
outputBytes[outputLength++] = '\n';
}
}
//handle left-over data
if (i == inputLength - 2)
{
// = terminator
outputBytes[outputLength++] = lookup[(inputBytes[i] & 0xFC) >> 2];
outputBytes[outputLength++] = lookup[((inputBytes[i] & 0x03) << 4) | ((inputBytes[i + 1] & 0xF0) >> 4)];
outputBytes[outputLength++] = lookup[(inputBytes[i + 1] & 0x0F) << 2];
outputBytes[outputLength++] = '=';
}
else if (i == inputLength - 1)
{
// == terminator
outputBytes[outputLength++] = lookup[(inputBytes[i] & 0xFC) >> 2];
outputBytes[outputLength++] = lookup[(inputBytes[i] & 0x03) << 4];
outputBytes[outputLength++] = '=';
outputBytes[outputLength++] = '=';
}
if (outputLength >= 4)
{
//truncate data to match actual output length
outputBytes = realloc(outputBytes, outputLength);
return [[NSString alloc] initWithBytesNoCopy:outputBytes
length:outputLength
encoding:NSASCIIStringEncoding
freeWhenDone:YES];
}
else if (outputBytes)
{
free(outputBytes);
}
returnnil;
}
- (NSString *)base64EncodedString
{
return [selfbase64EncodedStringWithWrapWidth:0];
}
@end
