Merge "Adjust minimum size of PKCS#1 RSA padding overhead." into mnc-dev

        // Constraints:

        // 1. Key must be authorized for signing without user authentication.

        // 2. Signature digest must be one of key's authorized digests.

        // 3. For RSA keys, the digest output size must not exceed modulus size minus space needed

        //    for RSA PKCS#1 signature padding (about 29 bytes: minimum 10 bytes of padding + 15--19

        //    bytes overhead for encoding digest OID and digest value in DER).

        // 3. For RSA keys, the digest output size must not exceed modulus size minus space overhead

        //    of RSA PKCS#1 signature padding scheme (about 30 bytes).

        // 4. For EC keys, the there is no point in using a digest whose output size is longer than

        //    key/field size because the digest will be truncated to that size.

                        spec.getDigests(),

                        AndroidKeyStoreBCWorkaroundProvider.getSupportedEcdsaSignatureDigests());

                // The amount of space available for the digest is less than modulus size because

                // padding must be at least 10 bytes long, and then there's also the 15--19

                // bytes overhead for encoding digest OID and digest value in DER.

                int maxDigestOutputSizeBits = keySizeBits - 29 * 8;

                // The amount of space available for the digest is less than modulus size by about

                // 30 bytes because padding must be at least 11 bytes long (00 || 01 || PS || 00,

                // where PS must be at least 8 bytes long), and then there's also the 15--19 bytes

                // overhead (depending the on chosen digest) for encoding digest OID and digest

                // value in DER.

                int maxDigestOutputSizeBits = keySizeBits - 30 * 8;

                int bestKeymasterDigest = -1;

                int bestDigestOutputSizeBits = -1;

                for (int keymasterDigest : availableKeymasterDigests) {