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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 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.

    /// RSA PKCS#1 1.5 signatures.

    use core;
    use {bits, digest, error, private, signature};
    use super::{bigint, N, PUBLIC_KEY_PUBLIC_MODULUS_MAX_LEN, RSAParameters,
                parse_public_key};
    use untrusted;

    impl signature::VerificationAlgorithm for RSAParameters {
        fn verify(&self, public_key: untrusted::Input, msg: untrusted::Input,
                  signature: untrusted::Input)
                  -> Result<(), error::Unspecified> {
            let public_key = parse_public_key(public_key)?;
            verify_rsa(self, public_key, msg, signature)
        }
    }

    impl private::Private for RSAParameters {}

    impl core::fmt::Debug for RSAParameters {
        fn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> {
            use super::RSAParametersID::*;
            // XXX: This doesn't include the padding algorithm nor the size range.
            write!(f, "ring::signature::{}", match self.id {
                RSA_PKCS1_2048_8192_SHA1 => "RSA_PKCS1_2048_8192_SHA1",
                RSA_PKCS1_2048_8192_SHA256 => "RSA_PKCS1_2048_8192_SHA256",
                RSA_PKCS1_2048_8192_SHA384 => "RSA_PKCS1_2048_8192_SHA384",
                RSA_PKCS1_2048_8192_SHA512 => "RSA_PKCS1_2048_8192_SHA512",
                RSA_PKCS1_3072_8192_SHA384 => "RSA_PKCS1_3072_8192_SHA384",
                RSA_PSS_2048_8192_SHA256 => "RSA_PSS_2048_8192_SHA256",
                RSA_PSS_2048_8192_SHA384 => "RSA_PSS_2048_8192_SHA384",
                RSA_PSS_2048_8192_SHA512 => "RSA_PSS_2048_8192_SHA512",
            })
        }
    }

    macro_rules! rsa_params {
        ( $VERIFY_ALGORITHM:ident, $min_bits:expr, $PADDING_ALGORITHM:expr,
          $doc_str:expr ) => {
            #[doc=$doc_str]
            ///
            /// Only available in `use_heap` mode.
            pub static $VERIFY_ALGORITHM: RSAParameters =
                RSAParameters {
                    padding_alg: $PADDING_ALGORITHM,
                    min_bits: bits::BitLength($min_bits),
                    id: super::RSAParametersID::$VERIFY_ALGORITHM,
                };
        }
    }

    rsa_params!(RSA_PKCS1_2048_8192_SHA1, 2048, &super::padding::RSA_PKCS1_SHA1,
                "Verification of signatures using RSA keys of 2048-8192 bits,
                 PKCS#1.5 padding, and SHA-1.\n\nSee \"`RSA_PKCS1_*` Details\" in
                 `ring::signature`'s module-level documentation for more details.");
    rsa_params!(RSA_PKCS1_2048_8192_SHA256, 2048, &super::RSA_PKCS1_SHA256,
                "Verification of signatures using RSA keys of 2048-8192 bits,
                 PKCS#1.5 padding, and SHA-256.\n\nSee \"`RSA_PKCS1_*` Details\" in
                 `ring::signature`'s module-level documentation for more details.");
    rsa_params!(RSA_PKCS1_2048_8192_SHA384, 2048, &super::RSA_PKCS1_SHA384,
                "Verification of signatures using RSA keys of 2048-8192 bits,
                 PKCS#1.5 padding, and SHA-384.\n\nSee \"`RSA_PKCS1_*` Details\" in
                 `ring::signature`'s module-level documentation for more details.");
    rsa_params!(RSA_PKCS1_2048_8192_SHA512, 2048, &super::RSA_PKCS1_SHA512,
                "Verification of signatures using RSA keys of 2048-8192 bits,
                 PKCS#1.5 padding, and SHA-512.\n\nSee \"`RSA_PKCS1_*` Details\" in
                 `ring::signature`'s module-level documentation for more details.");
    rsa_params!(RSA_PKCS1_3072_8192_SHA384, 3072, &super::RSA_PKCS1_SHA384,
                "Verification of signatures using RSA keys of 3072-8192 bits,
                 PKCS#1.5 padding, and SHA-384.\n\nSee \"`RSA_PKCS1_*` Details\" in
                 `ring::signature`'s module-level documentation for more details.");

    rsa_params!(RSA_PSS_2048_8192_SHA256, 2048, &super::RSA_PSS_SHA256,
                "Verification of signatures using RSA keys of 2048-8192 bits,
                 PSS padding, and SHA-256.\n\nSee \"`RSA_PSS_*` Details\" in
                 `ring::signature`'s module-level documentation for more details.");
    rsa_params!(RSA_PSS_2048_8192_SHA384, 2048, &super::RSA_PSS_SHA384,
                "Verification of signatures using RSA keys of 2048-8192 bits,
                 PSS padding, and SHA-384.\n\nSee \"`RSA_PSS_*` Details\" in
                 `ring::signature`'s module-level documentation for more details.");
    rsa_params!(RSA_PSS_2048_8192_SHA512, 2048, &super::RSA_PSS_SHA512,
                "Verification of signatures using RSA keys of 2048-8192 bits,
                 PSS padding, and SHA-512.\n\nSee \"`RSA_PSS_*` Details\" in
                 `ring::signature`'s module-level documentation for more details.");

    /// Lower-level API for the verification of RSA signatures.
    ///
    /// When the public key is in DER-encoded PKCS#1 ASN.1 format, it is
    /// recommended to use `ring::signature::verify()` with
    /// `ring::signature::RSA_PKCS1_*`, because `ring::signature::verify()`
    /// will handle the parsing in that case. Otherwise, this function can be used
    /// to pass in the raw bytes for the public key components as
    /// `untrusted::Input` arguments.
    ///
    /// `params` determine what algorithm parameters (padding, digest algorithm,
    /// key length range, etc.) are used in the verification. `msg` is the message
    /// and `signature` is the signature.
    ///
    /// `n` is the public key modulus and `e` is the public key exponent. Both are
    /// interpreted as unsigned big-endian encoded values. Both must be positive
    /// and neither may have any leading zeros.
    //
    // There are a small number of tests that test `verify_rsa` directly, but the
    // test coverage for this function mostly depends on the test coverage for the
    // `signature::VerificationAlgorithm` implementation for `RSAParameters`. If we
    // change that, test coverage for `verify_rsa()` will need to be reconsidered.
    // (The NIST test vectors were originally in a form that was optimized for
    // testing `verify_rsa` directly, but the testing work for RSA PKCS#1
    // verification was done during the implementation of
    // `signature::VerificationAlgorithm`, before `verify_rsa` was factored out).
    pub fn verify_rsa(params: &RSAParameters,
                      (n, e): (untrusted::Input, untrusted::Input),
                      msg: untrusted::Input, signature: untrusted::Input)
                      -> Result<(), error::Unspecified> {
        // Partially validate the public key. See
        // `check_public_modulus_and_exponent()` for more details.
        let n = bigint::Positive::from_be_bytes(n)?;
        let e = bigint::Positive::from_be_bytes(e)?;
        let max_bits = bits::BitLength::from_usize_bytes(
            PUBLIC_KEY_PUBLIC_MODULUS_MAX_LEN)?;

        // XXX: FIPS 186-4 seems to indicate that the minimum
        // exponent value is 2**16 + 1, but it isn't clear if this is just for
        // signing or also for verification. We support exponents of 3 and larger
        // for compatibility with other commonly-used crypto libraries.
        let e_min_bits = bits::BitLength::from_usize_bits(2);

        let (n, e) =
            super::check_public_modulus_and_exponent(n, e, params.min_bits, max_bits,
                                                     e_min_bits)?;
        let n_bits = n.bit_length();
        let n = n.into_modulus::<N>()?;

        // The signature must be the same length as the modulus, in bytes.
        if signature.len() != n_bits.as_usize_bytes_rounded_up() {
            return Err(error::Unspecified);
        }

        // RFC 8017 Section 5.2.2: RSAVP1.

        // Step 1.
        let s = bigint::Positive::from_be_bytes_padded(signature)?;
        let s = s.into_elem::<N>(&n)?;

        // Step 2.
        let s = {
            // Montgomery encode `s`.
            let oneRR = bigint::One::newRR(&n)?;
            bigint::elem_mul(oneRR.as_ref(), s, &n)?
        };
        let m = bigint::elem_exp_vartime(s, e, &n)?;
        let m = m.into_unencoded(&n)?;

        // Step 3.
        let mut decoded = [0u8; PUBLIC_KEY_PUBLIC_MODULUS_MAX_LEN];
        let decoded = &mut decoded[..n_bits.as_usize_bytes_rounded_up()];
        m.fill_be_bytes(decoded);

        // Verify the padded message is correct.
        let m_hash = digest::digest(params.padding_alg.digest_alg(),
                                    msg.as_slice_less_safe());
        untrusted::Input::from(decoded).read_all(
            error::Unspecified, |m| params.padding_alg.verify(&m_hash, m, n_bits))
    }

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