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    // Copyright 2015-2016 Brian Smith.
    //
    // Permission to use, copy, modify, and/or distribute this software for any
    // purpose with or without fee is hereby granted, provided that the above
    // copyright notice and this permission notice appear in all copies.
    //
    // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
    // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
    // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
    // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
    // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
    // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

    use {aead, bssl, c, error, polyfill};

    /// AES-128 in GCM mode with 128-bit tags and 96 bit nonces.
    ///
    /// C analog: `EVP_aead_aes_128_gcm`
    ///
    /// Go analog: [`crypto.aes`](https://golang.org/pkg/crypto/aes/)
    pub static AES_128_GCM: aead::Algorithm = aead::Algorithm {
        key_len: AES_128_KEY_LEN,
        init: aes_gcm_init,
        seal: aes_gcm_seal,
        open: aes_gcm_open,
    };

    /// AES-256 in GCM mode with 128-bit tags and 96 bit nonces.
    ///
    /// C analog: `EVP_aead_aes_256_gcm`
    ///
    /// Go analog: [`crypto.aes`](https://golang.org/pkg/crypto/aes/)
    pub static AES_256_GCM: aead::Algorithm = aead::Algorithm {
        key_len: AES_256_KEY_LEN,
        init: aes_gcm_init,
        seal: aes_gcm_seal,
        open: aes_gcm_open,
    };

    fn aes_gcm_init(ctx_buf: &mut [u8], key: &[u8])
                    -> Result<(), error::Unspecified> {
        bssl::map_result(unsafe {
            GFp_aes_gcm_init(ctx_buf.as_mut_ptr(), ctx_buf.len(), key.as_ptr(),
                             key.len())
        })
    }

    fn aes_gcm_seal(ctx: &[u64; aead::KEY_CTX_BUF_ELEMS],
                    nonce: &[u8; aead::NONCE_LEN], ad: &[u8], in_out: &mut [u8],
                    tag: &mut [u8; aead::TAG_LEN])
                    -> Result<(), error::Unspecified> {
        let ctx = polyfill::slice::u64_as_u8(ctx);
        bssl::map_result(unsafe {
            GFp_aes_gcm_seal(ctx.as_ptr(), in_out.as_mut_ptr(), in_out.len(), tag,
                             nonce, ad.as_ptr(), ad.len())
        })
    }

    fn aes_gcm_open(ctx: &[u64; aead::KEY_CTX_BUF_ELEMS],
                    nonce: &[u8; aead::NONCE_LEN], ad: &[u8], in_prefix_len: usize,
                    in_out: &mut [u8], tag_out: &mut [u8; aead::TAG_LEN])
                    -> Result<(), error::Unspecified> {
        let ctx = polyfill::slice::u64_as_u8(ctx);
        bssl::map_result(unsafe {
            GFp_aes_gcm_open(ctx.as_ptr(), in_out.as_mut_ptr(),
                             in_out.len() - in_prefix_len, tag_out, nonce,
                             in_out[in_prefix_len..].as_ptr(), ad.as_ptr(),
                             ad.len())
        })
    }

    const AES_128_KEY_LEN: usize = 128 / 8;
    const AES_256_KEY_LEN: usize = 32; // 256 / 8

    pub const AES_KEY_CTX_BUF_LEN: usize = AES_KEY_BUF_LEN + GCM128_SERIALIZED_LEN;

    // Keep this in sync with `AES_KEY` in aes.h.
    const AES_KEY_BUF_LEN: usize = (4 * 4 * (AES_MAX_ROUNDS + 1)) + 8;

    // Keep this in sync with `AES_MAXNR` in aes.h.
    const AES_MAX_ROUNDS: usize = 14;

    // Keep this in sync with `GCM128_SERIALIZED_LEN` in gcm.h.
    // TODO: test.
    // TODO: some implementations of GCM don't require the buffer to be this big.
    // We should shrink it down on those platforms since this is still huge.
    const GCM128_SERIALIZED_LEN: usize = 16 * 16;

    extern {
        fn GFp_aes_gcm_init(ctx_buf: *mut u8, ctx_buf_len: c::size_t,
                            key: *const u8, key_len: c::size_t) -> c::int;

        fn GFp_aes_gcm_seal(ctx_buf: *const u8, in_out: *mut u8,
                            in_out_len: c::size_t,
                            tag_out: &mut [u8; aead::TAG_LEN],
                            nonce: &[u8; aead::NONCE_LEN], ad: *const u8,
                            ad_len: c::size_t) -> c::int;

        fn GFp_aes_gcm_open(ctx_buf: *const u8, out: *mut u8,
                            in_out_len: c::size_t,
                            tag_out: &mut [u8; aead::TAG_LEN],
                            nonce: &[u8; aead::NONCE_LEN], in_: *const u8,
                            ad: *const u8, ad_len: c::size_t) -> c::int;
    }

    #[cfg(test)]
    mod tests {
        use {c, test};
        use super::AES_MAX_ROUNDS;

        #[test]
        pub fn test_aes() {
            test::from_file("src/aead/aes_tests.txt", |section, test_case| {
                assert_eq!(section, "");
                let key = test_case.consume_bytes("Key");
                let input = test_case.consume_bytes("Input");
                let input = slice_as_array_ref!(&input, AES_BLOCK_SIZE).unwrap();
                let expected_output = test_case.consume_bytes("Output");
                let expected_output =
                    slice_as_array_ref!(&expected_output, AES_BLOCK_SIZE).unwrap();

                // Key setup.
                let mut aes_key = AES_KEY {
                    rd_key: [0u32; 4 * (AES_MAX_ROUNDS + 1)],
                    rounds: 0,
                };
                let res = unsafe {
                    GFp_AES_set_encrypt_key(key.as_ptr(), key.len() * 8,
                                            &mut aes_key)
                };
                assert_eq!(res, 0, "GFp_AES_set_encrypt_key failed.");

                // Test encryption into a separate buffer.
                let mut output_buf = [0u8; AES_BLOCK_SIZE];
                unsafe {
                    GFp_AES_encrypt(input.as_ptr(), output_buf.as_mut_ptr(),
                                    &aes_key);
                }
                assert_eq!(&output_buf[..], &expected_output[..]);

                // Test in-place encryption.
                output_buf.copy_from_slice(&input[..]);
                unsafe {
                    GFp_AES_encrypt(output_buf.as_ptr(), output_buf.as_mut_ptr(),
                                    &aes_key);
                }
                assert_eq!(&output_buf[..], &expected_output[..]);

                Ok(())
            })
        }

        const AES_BLOCK_SIZE: usize = 16;

        // Keep this in sync with AES_KEY in aes.h.
        #[repr(C)]
        pub struct AES_KEY {
            pub rd_key: [u32; 4 * (AES_MAX_ROUNDS + 1)],
            pub rounds: usize,
        }

        extern "C" {
            fn GFp_AES_set_encrypt_key(key: *const u8, bits: usize,
                                       aes_key: *mut AES_KEY) -> c::int;
            fn GFp_AES_encrypt(in_: *const u8, out: *mut u8, key: *const AES_KEY);
        }
    }

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