swiftでS3のマルチパートアップロード時のETagを計算する ref: http://qiita.com/ikeisuke/items/8222899dd0742112680d

extensions.swift

extension NSData {
    func s3etag(minimumPartSize: UInt64 = 5 * 1024 * 1024) -> String {
        func md5digest(data: NSData) -> NSData {
            let digestLength = Int(CC_MD5_DIGEST_LENGTH)
            let md5Buffer = UnsafeMutablePointer<CUnsignedChar>.alloc(digestLength)

            CC_MD5(data.bytes, CC_LONG(data.length), md5Buffer)
            return NSMutableData(bytesNoCopy: md5Buffer, length: digestLength)
        }
        func md5hexdigext(data: NSData) -> String {
            let digestLength = Int(CC_MD5_DIGEST_LENGTH)
            let md5Buffer = UnsafeMutablePointer<CUnsignedChar>.alloc(digestLength)
            CC_MD5(data.bytes, CC_LONG(data.length), md5Buffer)
            var output = NSMutableString(capacity: Int(CC_MD5_DIGEST_LENGTH * 2))
            for i in 0..<digestLength {
                output.appendFormat("%02x", md5Buffer[i])
            }
            return String(format: output)
        }
        var size = UInt64(self.length)
        if size > minimumPartSize {
            var md5s = NSMutableData()
            var partCount = UInt64((size + (minimumPartSize / 2)) / minimumPartSize)
            for var i:UInt64=0; i<partCount; i++ {
                var dataStart  = Int(i * minimumPartSize);
                var dataLength = Int((i == (partCount - 1)) ? (size - (i * minimumPartSize)) : minimumPartSize)
                md5s.appendData(md5digest(self.subdataWithRange(NSMakeRange(dataStart, dataLength))))
            }
            return md5hexdigext(md5s) + "-" + String(partCount);
        } else {
            return md5hexdigext(self)
        }
    }
}

project-Bridging-Header.h

#import <CommonCrypto/CommonCrypto.h>