问题
I am trying to access Amazon's Product Advertising API in my iOS application. Creating the signature seems to be the tough part. On this page:
http://docs.amazonwebservices.com/AWSECommerceService/latest/DG/rest-signature.html
It says to "Calculate an RFC 2104-compliant HMAC with the SHA256 hash algorithm". Amazon also provides a java class to do this for you:
http://docs.amazonwebservices.com/AWSECommerceService/latest/DG/AuthJavaSampleSig2.html
Does anybody know how I can do this in Objective-C instead? I looked into the AWS iOS SDK, but it doesn't seem to include the Product Advertising API.
回答1:
Actually the AWS iOS SDK DID have a static method to handle all auth situations.
Maybe you should take a glance at the AmazonAuthUtils.h :
+(NSString *)HMACSign:(NSData *)data withKey:(NSString *)key usingAlgorithm:(CCHmacAlgorithm)algorithm;
+(NSData *)sha256HMac:(NSData *)data withKey:(NSString *)key;
you can find it in the document: http://docs.amazonwebservices.com/AWSiOSSDK/latest/Classes/AmazonAuthUtils.html
回答2:
Just to add a bit to camelcc's excellent observation. This does indeed work well for signing requests to the Amazon Product Advertising API. I had to mess around a bit to get it working.
Get the SDK installed and #import <AWSiOSSDK/AmazonAuthUtils.h>
First you've got to organize the request string into the correct order, as per the Amazon docs. I found this page very useful in explaining how to order the request
http://skilldrick.co.uk/2010/02/amazon-product-information-via-amazon-web-services/
Note the need for new-line characters in the string, my unsigned string looked like this
@"GET\necs.amazonaws.com\n/onca/xml\nAWSAccessKeyId=<ACCESS_KEY_ID>&AssociateTag=<ASSOCIATE_ID>&Keywords=harry%20potter&Operation=ItemSearch&SearchIndex=Books&Service=AWSECommerceService&Timestamp=2012-07-03T10%3A52%3A21.000Z&Version=2011-08-01"
No spaces anywhere, but \n characters in the right places. The convert this to NSData like so
NSData *dataToSign = [unsignedString dataUsingEncoding:NSUTF8StringEncoding];
Then call
[AmazonAuthUtils HMACSign:dataToSign withKey:SECRET_KEY usingAlgorithm:kCCHmacAlgSHA256]
This returns your signature as an NSString. You'll need to URL encode this (ie swapping illegal/unsafe charecters for %0x symbols (ie '=' converts to '%3D'))
Once this is done, stick it in your request and hopefully you are good to go!
回答3:
Check out my Amazon Product Advertising Client https://github.com/m1entus/RWMAmazonProductAdvertisingManager
Some code with requesst serialization:
NSString * const RWMAmazonProductAdvertisingStandardRegion = @"webservices.amazon.com";
NSString * const RWMAmazonProductAdvertisingAWSAccessKey = @"AWSAccessKeyId";
NSString * const RWMAmazonProductAdvertisingTimestampKey = @"Timestamp";
NSString * const RWMAmazonProductAdvertisingSignatureKey = @"Signature";
NSString * const RWMAmazonProductAdvertisingVersionKey = @"Version";
NSString * const RWMAmazonProductAdvertisingCurrentVersion = @"2011-08-01";
NSData * RWMHMACSHA256EncodedDataFromStringWithKey(NSString *string, NSString *key) {
NSData *data = [string dataUsingEncoding:NSASCIIStringEncoding];
CCHmacContext context;
const char *keyCString = [key cStringUsingEncoding:NSASCIIStringEncoding];
CCHmacInit(&context, kCCHmacAlgSHA256, keyCString, strlen(keyCString));
CCHmacUpdate(&context, [data bytes], [data length]);
unsigned char digestRaw[CC_SHA256_DIGEST_LENGTH];
NSUInteger digestLength = CC_SHA256_DIGEST_LENGTH;
CCHmacFinal(&context, digestRaw);
return [NSData dataWithBytes:digestRaw length:digestLength];
}
NSString * RWMISO8601FormatStringFromDate(NSDate *date) {
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"GMT"]];
[dateFormatter setDateFormat:@"YYYY-MM-dd'T'HH:mm:ss'Z'"];
[dateFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"]];
return [dateFormatter stringFromDate:date];
}
NSString * RWMBase64EncodedStringFromData(NSData *data) {
#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 70000
return [data base64EncodedStringWithOptions:0];
#else
return [data base64Encoding];
#endif
}
//http://docs.aws.amazon.com/AWSECommerceService/latest/DG/rest-signature.html
- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request
withParameters:(id)parameters
error:(NSError * __autoreleasing *)error
{
NSParameterAssert(request);
NSMutableURLRequest *mutableRequest = [request mutableCopy];
if (self.accessKey && self.secret) {
NSMutableDictionary *mutableParameters = [parameters mutableCopy];
NSString *timestamp = RWMISO8601FormatStringFromDate([NSDate date]);
if (!mutableParameters[RWMAmazonProductAdvertisingAWSAccessKey]) {
[mutableParameters setObject:self.accessKey forKey:RWMAmazonProductAdvertisingAWSAccessKey];
}
mutableParameters[RWMAmazonProductAdvertisingVersionKey] = RWMAmazonProductAdvertisingCurrentVersion;
mutableParameters[RWMAmazonProductAdvertisingTimestampKey] = timestamp;
NSMutableArray *canonicalStringArray = [[NSMutableArray alloc] init];
for (NSString *key in [[mutableParameters allKeys] sortedArrayUsingSelector:@selector(compare:)]) {
id value = [mutableParameters objectForKey:key];
[canonicalStringArray addObject:[NSString stringWithFormat:@"%@=%@", key, value]];
}
NSString *canonicalString = [canonicalStringArray componentsJoinedByString:@"&"];
canonicalString = CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
(__bridge CFStringRef)canonicalString,
NULL,
CFSTR(":,"),
kCFStringEncodingUTF8));
NSString *method = [request HTTPMethod];
NSString *signature = [NSString stringWithFormat:@"%@\n%@\n%@\n%@",method,self.region,self.formatPath,canonicalString];
NSData *encodedSignatureData = RWMHMACSHA256EncodedDataFromStringWithKey(signature,self.secret);
NSString *encodedSignatureString = RWMBase64EncodedStringFromData(encodedSignatureData);
encodedSignatureString = CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
(__bridge CFStringRef)encodedSignatureString,
NULL,
CFSTR("+="),
kCFStringEncodingUTF8));
canonicalString = [canonicalString stringByAppendingFormat:@"&%@=%@",RWMAmazonProductAdvertisingSignatureKey,encodedSignatureString];
mutableRequest.URL = [NSURL URLWithString:[[mutableRequest.URL absoluteString] stringByAppendingFormat:mutableRequest.URL.query ? @"&%@" : @"?%@", canonicalString]];
} else {
if (error) {
NSDictionary *userInfo = @{NSLocalizedDescriptionKey: NSLocalizedStringFromTable(@"Access Key and Secret Required", @"RWMAmazonProductAdvertisingManager", nil)};
*error = [[NSError alloc] initWithDomain:RWMAmazonProductAdvertisingManagerErrorDomain code:NSURLErrorUserAuthenticationRequired userInfo:userInfo];
}
}
return mutableRequest;
}
回答4:
Thanks for all answers on this page. Here is what has worked for me (Swift 3.0):
Podfile:
pod 'AWSAPIGateway', '~> 2.4.7'
Swift code
static let kAmazonAccessID = "BLAH BLAH BLAH"
static let kAmazonAccessSecretKey = "BLAH BLAH BLAH"
static let kAmazonAssociateTag = "BLAH BLAH BLAH"
private let timestampFormatter: DateFormatter
init() {
timestampFormatter = DateFormatter()
timestampFormatter.timeZone = TimeZone(identifier: "GMT")
timestampFormatter.dateFormat = "YYYY-MM-dd'T'HH:mm:ss'Z'"
timestampFormatter.locale = Locale(identifier: "en_US_POSIX")
}
private func signedParametersForParameters(parameters: [String: String]) -> [String: String] {
let sortedKeys = Array(parameters.keys).sorted(by: <)
let query = sortedKeys.map { String(format: "%@=%@", $0, parameters[$0] ?? "") }.joined(separator: "&")
let stringToSign = "GET\nwebservices.amazon.com\n/onca/xml\n\(query)"
let dataToSign = stringToSign.data(using: String.Encoding.utf8)
let signature = AWSSignatureSignerUtility.hmacSign(dataToSign, withKey: AmazonAPI.kAmazonAccessSecretKey, usingAlgorithm: UInt32(kCCHmacAlgSHA256))!
var signedParams = parameters;
signedParams["Signature"] = urlEncode(signature)
return signedParams
}
public func urlEncode(_ input: String) -> String {
let allowedCharacterSet = (CharacterSet(charactersIn: "!*'();:@&=+$,/?%#[] ").inverted)
if let escapedString = input.addingPercentEncoding(withAllowedCharacters: allowedCharacterSet) {
return escapedString
}
return ""
}
func send(url: String) -> String {
guard let url = URL(string: url) else {
print("Error! Invalid URL!") //Do something else
return ""
}
let request = URLRequest(url: url)
let semaphore = DispatchSemaphore(value: 0)
var data: Data? = nil
URLSession.shared.dataTask(with: request) { (responseData, _, _) -> Void in
data = responseData
semaphore.signal()
}.resume()
semaphore.wait(timeout: .distantFuture)
let reply = data.flatMap { String(data: $0, encoding: .utf8) } ?? ""
return reply
}
and here is the function that ask Amazon for price of a product:
public func getProductPrice(_ asin: AmazonStandardIdNumber) -> Double {
let operationParams: [String: String] = [
"Service": "AWSECommerceService",
"Operation": "ItemLookup",
"ResponseGroup": "Offers",
"IdType": "ASIN",
"ItemId": asin,
"AWSAccessKeyId": urlEncode(AmazonAPI.kAmazonAccessID),
"AssociateTag": urlEncode(AmazonAPI.kAmazonAssociateTag),
"Timestamp": urlEncode(timestampFormatter.string(from: Date())),]
let signedParams = signedParametersForParameters(parameters: operationParams)
let query = signedParams.map { "\($0)=\($1)" }.joined(separator: "&")
let url = "http://webservices.amazon.com/onca/xml?" + query
let reply = send(url: url)
// USE THE RESPONSE
}
回答5:
A few steps missing from P-double post.
Prior to constructing the unsigned string, you will need to get the Timestamp value in place.
NSTimeZone *zone = [NSTimeZone defaultTimeZone]; //get the current application default time zone
NSInteger interval = [zone secondsFromGMTForDate:[NSDate date]];//sec Returns the time difference of the current application with the world standard time (Green Venice time)
NSDate *nowDate = [NSDate dateWithTimeIntervalSinceNow:interval];
NSDateFormatter * formatter = [[NSDateFormatter alloc] init];
[formatter setTimeZone:[NSTimeZone systemTimeZone]];// get current date/time
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setTimeZone:[NSTimeZone systemTimeZone]];
// display in 12HR/24HR (i.e. 11:25PM or 23:25) format according to User Settings
[dateFormatter setDateFormat:@"yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'"];
NSString *currentTime = [dateFormatter stringFromDate:nowDate];
NSString* encodedTime = (NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(NULL, (__bridge CFStringRef) currentTime,NULL, CFSTR("!*'();:@&=+$,/?%#[]"),kCFStringEncodingUTF8));
NSString* unsignedString = [NSString stringWithFormat:@"GET\nwebservices.amazon.com\n/onca/xml\nAWSAccessKeyId=AKIAI443QEMWI6KW55QQ&AssociateTag=sajjmanz-20&Condition=All&IdType=ASIN&ItemId=3492264077&Operation=ItemLookup&ResponseGroup=Images%%2CItemAttributes%%2COffers&Service=AWSECommerceService&Timestamp=%@&Version=2011-08-01", encodedTime];
Once the date is url friendly encoded, the rest of the steps works like a charm.
Lastly, I also used CFURLCreateStringByAddingPercentEscapes listed above to encode the string generated by the AmazonAuthUtils HMACSign message call.
回答6:
Am I wrong that it is not 'legal' (according to Amazon's own guidelines) to use Amazon's Product Advertising API in an iOS app without Amazon's express written consent?
回答7:
Swift 2.0
Here is a function that will sign a set of parameters for Swift. Note that this code requires the Alamofire and AWSCore Cocoapods to be installed. You also need to add #import <CommonCrypto/CommonCrypto.h> to your Objective-C Bridging header otherwise kCCHmacAlgSHA256 won't be found.
private func signedParametersForParameters(parameters: [String: String]) -> [String: String] {
let sortedKeys = Array(parameters.keys).sort(<)
var components: [(String, String)] = []
for key in sortedKeys {
components += ParameterEncoding.URLEncodedInURL.queryComponents(key, parameters[key]!)
}
let query = (components.map { "\($0)=\($1)" } as [String]).joinWithSeparator("&")
let stringToSign = "GET\nwebservices.amazon.com\n/onca/xml\n\(query)"
let dataToSign = stringToSign.dataUsingEncoding(NSUTF8StringEncoding)
let signature = AWSSignatureSignerUtility.HMACSign(dataToSign, withKey: kAmazonAccessSecretKey, usingAlgorithm: UInt32(kCCHmacAlgSHA256))!
let signedParams = parameters + ["Signature": signature]
return signedParams
}
It's called like this:
let operationParams: [String: String] = ["Service": "AWSECommerceService", "Operation": "ItemLookup", "ItemId": "045242127733", "IdType": "UPC", "ResponseGroup": "Images,ItemAttributes", "SearchIndex": "All"]
let keyParams = ["AWSAccessKeyId": kAmazonAccessID, "AssociateTag": kAmazonAssociateTag, "Timestamp": timestampFormatter.stringFromDate(NSDate())]
let fullParams = operationParams + keyParams
let signedParams = signedParametersForParameters(fullParams)
Alamofire.request(.GET, "http://webservices.amazon.com/onca/xml", parameters: signedParams).responseString { (response) in
print("Success: \(response.result.isSuccess)")
print("Response String: \(response.result.value)")
}
Finally, the timestampFormatter is declared like this:
private let timestampFormatter: NSDateFormatter
init() {
timestampFormatter = NSDateFormatter()
timestampFormatter.dateFormat = AWSDateISO8601DateFormat3
timestampFormatter.timeZone = NSTimeZone(name: "GMT")
timestampFormatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
}
You can use/modify to suit your needs, but everything that's necessary should be there.
回答8:
Instead of using CommonCrypto, which is deprecated in modern OS X, you can also use SecTransforms:
CFErrorRef error = NULL;
SecTransformRef digestRef = SecDigestTransformCreate(kSecDigestHMACSHA2, 256, &error);
SecTransformSetAttribute(digestRef, kSecTransformInputAttributeName, (__bridge CFDataRef)self, &error);
SecTransformSetAttribute(digestRef, kSecDigestHMACKeyAttribute, (__bridge CFDataRef)key, &error);
CFDataRef resultData = SecTransformExecute(digestRef, &error);
NSData* hashData = (__bridge NSData*)resultData;
CFRelease(digestRef);
来源：https://stackoverflow.com/questions/10940271/amazon-product-advertising-api-signature-in-ios