iOS 9 app download from Amazon S3 SSL error: TLS 1.2 support

Edit 2016-01-03: The renewed certificate for s3.amazonaws.com uses the SHA256 algorithm and complies with ATS requirements.

Original answer: s3.amazonaws.com uses a SHA1 cerificate that does not meet ATS requirements, resulting in a hard failure. Per the App Transport Security Technote, ATS in iOS9 has the following requirements:

1. The server must support at least Transport Layer Security (TLS) protocol version 1.2.

2. Connection ciphers are limited to those that provide forward secrecy, namely,

   TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
   TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
   TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384
   TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA
   TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256
   TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA
   TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
   TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384
   TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
   TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA

3. Certificates must be signed using a SHA256 or better signature hash algorithm, with either a 2048 bit or greater RSA key or a 256 bit or greater Elliptic-Curve (ECC) key.

Invalid certificates result in a hard failure and no connection.

SSL Labs’ SSL server test (https://www.ssllabs.com/ssltest/analyze.html?d=s3.amazonaws.com) includes a handshake simulation for ATS in iOS 9 that indicates a failure for s3.amazonaws.com.