// This file was stolen from rust-crypto.
// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

#[cfg(not(fuzzing))]
mod real_chacha {
    use core::cmp;
    use core::convert::TryInto;

    #[derive(Clone, Copy, PartialEq, Eq)]
    #[allow(non_camel_case_types)]
    struct u32x4(pub u32, pub u32, pub u32, pub u32);
    impl ::core::ops::Add for u32x4 {
        type Output = u32x4;
        fn add(self, rhs: u32x4) -> u32x4 {
            u32x4(
                self.0.wrapping_add(rhs.0),
                self.1.wrapping_add(rhs.1),
                self.2.wrapping_add(rhs.2),
                self.3.wrapping_add(rhs.3),
            )
        }
    }
    impl ::core::ops::Sub for u32x4 {
        type Output = u32x4;
        fn sub(self, rhs: u32x4) -> u32x4 {
            u32x4(
                self.0.wrapping_sub(rhs.0),
                self.1.wrapping_sub(rhs.1),
                self.2.wrapping_sub(rhs.2),
                self.3.wrapping_sub(rhs.3),
            )
        }
    }
    impl ::core::ops::BitXor for u32x4 {
        type Output = u32x4;
        fn bitxor(self, rhs: u32x4) -> u32x4 {
            u32x4(self.0 ^ rhs.0, self.1 ^ rhs.1, self.2 ^ rhs.2, self.3 ^ rhs.3)
        }
    }
    impl ::core::ops::Shr<u32x4> for u32x4 {
        type Output = u32x4;
        fn shr(self, rhs: u32x4) -> u32x4 {
            u32x4(self.0 >> rhs.0, self.1 >> rhs.1, self.2 >> rhs.2, self.3 >> rhs.3)
        }
    }
    impl ::core::ops::Shl<u32x4> for u32x4 {
        type Output = u32x4;
        fn shl(self, rhs: u32x4) -> u32x4 {
            u32x4(self.0 << rhs.0, self.1 << rhs.1, self.2 << rhs.2, self.3 << rhs.3)
        }
    }
    impl u32x4 {
        fn from_bytes(bytes: &[u8]) -> Self {
            assert_eq!(bytes.len(), 4 * 4);
            Self(
                u32::from_le_bytes(bytes[0 * 4..1 * 4].try_into().expect("len is 4")),
                u32::from_le_bytes(bytes[1 * 4..2 * 4].try_into().expect("len is 4")),
                u32::from_le_bytes(bytes[2 * 4..3 * 4].try_into().expect("len is 4")),
                u32::from_le_bytes(bytes[3 * 4..4 * 4].try_into().expect("len is 4")),
            )
        }
    }

    const BLOCK_SIZE: usize = 64;

    #[derive(Clone, Copy)]
    struct ChaChaState {
        a: u32x4,
        b: u32x4,
        c: u32x4,
        d: u32x4,
    }

    #[derive(Copy)]
    pub struct ChaCha20 {
        state: ChaChaState,
        output: [u8; BLOCK_SIZE],
        offset: usize,
    }

    impl Clone for ChaCha20 {
        fn clone(&self) -> ChaCha20 {
            *self
        }
    }

    macro_rules! swizzle {
        ($b: expr, $c: expr, $d: expr) => {{
            let u32x4(b10, b11, b12, b13) = $b;
            $b = u32x4(b11, b12, b13, b10);
            let u32x4(c10, c11, c12, c13) = $c;
            $c = u32x4(c12, c13, c10, c11);
            let u32x4(d10, d11, d12, d13) = $d;
            $d = u32x4(d13, d10, d11, d12);
        }};
    }

    macro_rules! state_to_buffer {
        ($state: expr, $output: expr) => {{
            let u32x4(a1, a2, a3, a4) = $state.a;
            let u32x4(b1, b2, b3, b4) = $state.b;
            let u32x4(c1, c2, c3, c4) = $state.c;
            let u32x4(d1, d2, d3, d4) = $state.d;
            let lens = [a1, a2, a3, a4, b1, b2, b3, b4, c1, c2, c3, c4, d1, d2, d3, d4];
            for i in 0..lens.len() {
                $output[i * 4..(i + 1) * 4].copy_from_slice(&lens[i].to_le_bytes());
            }
        }};
    }

    macro_rules! round {
        ($state: expr) => {{
            $state.a = $state.a + $state.b;
            rotate!($state.d, $state.a, S16);
            $state.c = $state.c + $state.d;
            rotate!($state.b, $state.c, S12);
            $state.a = $state.a + $state.b;
            rotate!($state.d, $state.a, S8);
            $state.c = $state.c + $state.d;
            rotate!($state.b, $state.c, S7);
        }};
    }

    macro_rules! rotate {
        ($a: expr, $b: expr, $c:expr) => {{
            let v = $a ^ $b;
            let r = S32 - $c;
            let right = v >> r;
            $a = (v << $c) ^ right
        }};
    }

    const S32: u32x4 = u32x4(32, 32, 32, 32);
    const S16: u32x4 = u32x4(16, 16, 16, 16);
    const S12: u32x4 = u32x4(12, 12, 12, 12);
    const S8: u32x4 = u32x4(8, 8, 8, 8);
    const S7: u32x4 = u32x4(7, 7, 7, 7);

    impl ChaCha20 {
        pub fn new(key: &[u8], nonce: &[u8]) -> ChaCha20 {
            assert!(key.len() == 16 || key.len() == 32);
            assert!(nonce.len() == 8 || nonce.len() == 12);

            ChaCha20 { state: ChaCha20::expand(key, nonce), output: [0u8; BLOCK_SIZE], offset: 64 }
        }

        /// Get one block from a ChaCha stream.
        pub fn get_single_block(key: &[u8; 32], nonce: &[u8; 16]) -> [u8; 32] {
            let mut chacha = ChaCha20 {
                state: ChaCha20::expand(key, nonce),
                output: [0u8; BLOCK_SIZE],
                offset: 64,
            };
            let mut chacha_bytes = [0; 32];
            chacha.process_in_place(&mut chacha_bytes);
            chacha_bytes
        }

        fn expand(key: &[u8], nonce: &[u8]) -> ChaChaState {
            let constant = match key.len() {
                16 => b"expand 16-byte k",
                32 => b"expand 32-byte k",
                _ => unreachable!(),
            };
            ChaChaState {
                a: u32x4::from_bytes(&constant[0..16]),
                b: u32x4::from_bytes(&key[0..16]),
                c: if key.len() == 16 {
                    u32x4::from_bytes(&key[0..16])
                } else {
                    u32x4::from_bytes(&key[16..32])
                },
                d: if nonce.len() == 16 {
                    u32x4::from_bytes(&nonce[0..16])
                } else if nonce.len() == 12 {
                    let mut nonce4 = [0; 4 * 4];
                    nonce4[4..].copy_from_slice(nonce);
                    u32x4::from_bytes(&nonce4)
                } else {
                    let mut nonce4 = [0; 4 * 4];
                    nonce4[8..].copy_from_slice(nonce);
                    u32x4::from_bytes(&nonce4)
                },
            }
        }

        // put the the next BLOCK_SIZE keystream bytes into self.output
        fn update(&mut self) {
            let mut state = self.state;

            for _ in 0..10 {
                round!(state);
                swizzle!(state.b, state.c, state.d);
                round!(state);
                swizzle!(state.d, state.c, state.b);
            }
            state.a = state.a + self.state.a;
            state.b = state.b + self.state.b;
            state.c = state.c + self.state.c;
            state.d = state.d + self.state.d;

            state_to_buffer!(state, self.output);

            self.state.d = self.state.d + u32x4(1, 0, 0, 0);
            let u32x4(c12, _, _, _) = self.state.d;
            if c12 == 0 {
                // we could increment the other counter word with an 8 byte nonce
                // but other implementations like boringssl have this same
                // limitation
                panic!("counter is exhausted");
            }

            self.offset = 0;
        }

        #[inline] // Useful cause input may be 0s on stack that should be optimized out
        pub fn process(&mut self, input: &[u8], output: &mut [u8]) {
            assert!(input.len() == output.len());
            let len = input.len();
            let mut i = 0;
            while i < len {
                // If there is no keystream available in the output buffer,
                // generate the next block.
                if self.offset == BLOCK_SIZE {
                    self.update();
                }

                // Process the min(available keystream, remaining input length).
                let count = cmp::min(BLOCK_SIZE - self.offset, len - i);
                // explicitly assert lengths to avoid bounds checks:
                assert!(output.len() >= i + count);
                assert!(input.len() >= i + count);
                assert!(self.output.len() >= self.offset + count);
                for j in 0..count {
                    output[i + j] = input[i + j] ^ self.output[self.offset + j];
                }
                i += count;
                self.offset += count;
            }
        }

        pub fn process_in_place(&mut self, input_output: &mut [u8]) {
            let len = input_output.len();
            let mut i = 0;
            while i < len {
                // If there is no keystream available in the output buffer,
                // generate the next block.
                if self.offset == BLOCK_SIZE {
                    self.update();
                }

                // Process the min(available keystream, remaining input length).
                let count = cmp::min(BLOCK_SIZE - self.offset, len - i);
                // explicitly assert lengths to avoid bounds checks:
                assert!(input_output.len() >= i + count);
                assert!(self.output.len() >= self.offset + count);
                for j in 0..count {
                    input_output[i + j] ^= self.output[self.offset + j];
                }
                i += count;
                self.offset += count;
            }
        }

        #[cfg(test)]
        pub fn seek_to_block(&mut self, block_offset: u32) {
            self.state.d.0 = block_offset;
            self.update();
        }
    }
}
#[cfg(not(fuzzing))]
pub use self::real_chacha::ChaCha20;

#[cfg(fuzzing)]
mod fuzzy_chacha {
    pub struct ChaCha20 {}

    impl ChaCha20 {
        pub fn new(key: &[u8], nonce: &[u8]) -> ChaCha20 {
            assert!(key.len() == 16 || key.len() == 32);
            assert!(nonce.len() == 8 || nonce.len() == 12);
            Self {}
        }

        pub fn get_single_block(_key: &[u8; 32], _nonce: &[u8; 16]) -> [u8; 32] {
            [0; 32]
        }

        pub fn process(&mut self, input: &[u8], output: &mut [u8]) {
            output.copy_from_slice(input);
        }

        pub fn process_in_place(&mut self, _input_output: &mut [u8]) {}
    }
}
#[cfg(fuzzing)]
pub use self::fuzzy_chacha::ChaCha20;

#[cfg(test)]
mod test {
    use core::iter::repeat;

    use super::ChaCha20;
    use std::convert::TryInto;

    #[test]
    fn test_chacha20_256_tls_vectors() {
        struct TestVector {
            key: [u8; 32],
            nonce: [u8; 8],
            keystream: Vec<u8>,
        }
        // taken from http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-04
        let test_vectors = vec![
            TestVector {
                key: [
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                ],
                nonce: [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],
                keystream: vec![
                    0x76, 0xb8, 0xe0, 0xad, 0xa0, 0xf1, 0x3d, 0x90, 0x40, 0x5d, 0x6a, 0xe5, 0x53,
                    0x86, 0xbd, 0x28, 0xbd, 0xd2, 0x19, 0xb8, 0xa0, 0x8d, 0xed, 0x1a, 0xa8, 0x36,
                    0xef, 0xcc, 0x8b, 0x77, 0x0d, 0xc7, 0xda, 0x41, 0x59, 0x7c, 0x51, 0x57, 0x48,
                    0x8d, 0x77, 0x24, 0xe0, 0x3f, 0xb8, 0xd8, 0x4a, 0x37, 0x6a, 0x43, 0xb8, 0xf4,
                    0x15, 0x18, 0xa1, 0x1c, 0xc3, 0x87, 0xb6, 0x69, 0xb2, 0xee, 0x65, 0x86,
                ],
            },
            TestVector {
                key: [
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
                ],
                nonce: [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],
                keystream: vec![
                    0x45, 0x40, 0xf0, 0x5a, 0x9f, 0x1f, 0xb2, 0x96, 0xd7, 0x73, 0x6e, 0x7b, 0x20,
                    0x8e, 0x3c, 0x96, 0xeb, 0x4f, 0xe1, 0x83, 0x46, 0x88, 0xd2, 0x60, 0x4f, 0x45,
                    0x09, 0x52, 0xed, 0x43, 0x2d, 0x41, 0xbb, 0xe2, 0xa0, 0xb6, 0xea, 0x75, 0x66,
                    0xd2, 0xa5, 0xd1, 0xe7, 0xe2, 0x0d, 0x42, 0xaf, 0x2c, 0x53, 0xd7, 0x92, 0xb1,
                    0xc4, 0x3f, 0xea, 0x81, 0x7e, 0x9a, 0xd2, 0x75, 0xae, 0x54, 0x69, 0x63,
                ],
            },
            TestVector {
                key: [
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                ],
                nonce: [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01],
                keystream: vec![
                    0xde, 0x9c, 0xba, 0x7b, 0xf3, 0xd6, 0x9e, 0xf5, 0xe7, 0x86, 0xdc, 0x63, 0x97,
                    0x3f, 0x65, 0x3a, 0x0b, 0x49, 0xe0, 0x15, 0xad, 0xbf, 0xf7, 0x13, 0x4f, 0xcb,
                    0x7d, 0xf1, 0x37, 0x82, 0x10, 0x31, 0xe8, 0x5a, 0x05, 0x02, 0x78, 0xa7, 0x08,
                    0x45, 0x27, 0x21, 0x4f, 0x73, 0xef, 0xc7, 0xfa, 0x5b, 0x52, 0x77, 0x06, 0x2e,
                    0xb7, 0xa0, 0x43, 0x3e, 0x44, 0x5f, 0x41, 0xe3,
                ],
            },
            TestVector {
                key: [
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                ],
                nonce: [0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],
                keystream: vec![
                    0xef, 0x3f, 0xdf, 0xd6, 0xc6, 0x15, 0x78, 0xfb, 0xf5, 0xcf, 0x35, 0xbd, 0x3d,
                    0xd3, 0x3b, 0x80, 0x09, 0x63, 0x16, 0x34, 0xd2, 0x1e, 0x42, 0xac, 0x33, 0x96,
                    0x0b, 0xd1, 0x38, 0xe5, 0x0d, 0x32, 0x11, 0x1e, 0x4c, 0xaf, 0x23, 0x7e, 0xe5,
                    0x3c, 0xa8, 0xad, 0x64, 0x26, 0x19, 0x4a, 0x88, 0x54, 0x5d, 0xdc, 0x49, 0x7a,
                    0x0b, 0x46, 0x6e, 0x7d, 0x6b, 0xbd, 0xb0, 0x04, 0x1b, 0x2f, 0x58, 0x6b,
                ],
            },
            TestVector {
                key: [
                    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c,
                    0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19,
                    0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
                ],
                nonce: [0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07],
                keystream: vec![
                    0xf7, 0x98, 0xa1, 0x89, 0xf1, 0x95, 0xe6, 0x69, 0x82, 0x10, 0x5f, 0xfb, 0x64,
                    0x0b, 0xb7, 0x75, 0x7f, 0x57, 0x9d, 0xa3, 0x16, 0x02, 0xfc, 0x93, 0xec, 0x01,
                    0xac, 0x56, 0xf8, 0x5a, 0xc3, 0xc1, 0x34, 0xa4, 0x54, 0x7b, 0x73, 0x3b, 0x46,
                    0x41, 0x30, 0x42, 0xc9, 0x44, 0x00, 0x49, 0x17, 0x69, 0x05, 0xd3, 0xbe, 0x59,
                    0xea, 0x1c, 0x53, 0xf1, 0x59, 0x16, 0x15, 0x5c, 0x2b, 0xe8, 0x24, 0x1a, 0x38,
                    0x00, 0x8b, 0x9a, 0x26, 0xbc, 0x35, 0x94, 0x1e, 0x24, 0x44, 0x17, 0x7c, 0x8a,
                    0xde, 0x66, 0x89, 0xde, 0x95, 0x26, 0x49, 0x86, 0xd9, 0x58, 0x89, 0xfb, 0x60,
                    0xe8, 0x46, 0x29, 0xc9, 0xbd, 0x9a, 0x5a, 0xcb, 0x1c, 0xc1, 0x18, 0xbe, 0x56,
                    0x3e, 0xb9, 0xb3, 0xa4, 0xa4, 0x72, 0xf8, 0x2e, 0x09, 0xa7, 0xe7, 0x78, 0x49,
                    0x2b, 0x56, 0x2e, 0xf7, 0x13, 0x0e, 0x88, 0xdf, 0xe0, 0x31, 0xc7, 0x9d, 0xb9,
                    0xd4, 0xf7, 0xc7, 0xa8, 0x99, 0x15, 0x1b, 0x9a, 0x47, 0x50, 0x32, 0xb6, 0x3f,
                    0xc3, 0x85, 0x24, 0x5f, 0xe0, 0x54, 0xe3, 0xdd, 0x5a, 0x97, 0xa5, 0xf5, 0x76,
                    0xfe, 0x06, 0x40, 0x25, 0xd3, 0xce, 0x04, 0x2c, 0x56, 0x6a, 0xb2, 0xc5, 0x07,
                    0xb1, 0x38, 0xdb, 0x85, 0x3e, 0x3d, 0x69, 0x59, 0x66, 0x09, 0x96, 0x54, 0x6c,
                    0xc9, 0xc4, 0xa6, 0xea, 0xfd, 0xc7, 0x77, 0xc0, 0x40, 0xd7, 0x0e, 0xaf, 0x46,
                    0xf7, 0x6d, 0xad, 0x39, 0x79, 0xe5, 0xc5, 0x36, 0x0c, 0x33, 0x17, 0x16, 0x6a,
                    0x1c, 0x89, 0x4c, 0x94, 0xa3, 0x71, 0x87, 0x6a, 0x94, 0xdf, 0x76, 0x28, 0xfe,
                    0x4e, 0xaa, 0xf2, 0xcc, 0xb2, 0x7d, 0x5a, 0xaa, 0xe0, 0xad, 0x7a, 0xd0, 0xf9,
                    0xd4, 0xb6, 0xad, 0x3b, 0x54, 0x09, 0x87, 0x46, 0xd4, 0x52, 0x4d, 0x38, 0x40,
                    0x7a, 0x6d, 0xeb, 0x3a, 0xb7, 0x8f, 0xab, 0x78, 0xc9,
                ],
            },
        ];

        for tv in test_vectors.iter() {
            let mut c = ChaCha20::new(&tv.key, &tv.nonce);
            let input: Vec<u8> = repeat(0).take(tv.keystream.len()).collect();
            let mut output: Vec<u8> = repeat(0).take(input.len()).collect();
            c.process(&input[..], &mut output[..]);
            assert_eq!(output, tv.keystream);
        }
    }

    #[test]
    fn test_chacha20_256_tls_vectors_96_nonce() {
        struct TestVector {
            key: [u8; 32],
            nonce: [u8; 12],
            keystream: Vec<u8>,
        }
        // taken from http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-04
        let test_vectors = vec![
            TestVector {
                key: [
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                ],
                nonce: [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],
                keystream: vec![
                    0x76, 0xb8, 0xe0, 0xad, 0xa0, 0xf1, 0x3d, 0x90, 0x40, 0x5d, 0x6a, 0xe5, 0x53,
                    0x86, 0xbd, 0x28, 0xbd, 0xd2, 0x19, 0xb8, 0xa0, 0x8d, 0xed, 0x1a, 0xa8, 0x36,
                    0xef, 0xcc, 0x8b, 0x77, 0x0d, 0xc7, 0xda, 0x41, 0x59, 0x7c, 0x51, 0x57, 0x48,
                    0x8d, 0x77, 0x24, 0xe0, 0x3f, 0xb8, 0xd8, 0x4a, 0x37, 0x6a, 0x43, 0xb8, 0xf4,
                    0x15, 0x18, 0xa1, 0x1c, 0xc3, 0x87, 0xb6, 0x69, 0xb2, 0xee, 0x65, 0x86,
                ],
            },
            TestVector {
                key: [
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
                ],
                nonce: [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],
                keystream: vec![
                    0x45, 0x40, 0xf0, 0x5a, 0x9f, 0x1f, 0xb2, 0x96, 0xd7, 0x73, 0x6e, 0x7b, 0x20,
                    0x8e, 0x3c, 0x96, 0xeb, 0x4f, 0xe1, 0x83, 0x46, 0x88, 0xd2, 0x60, 0x4f, 0x45,
                    0x09, 0x52, 0xed, 0x43, 0x2d, 0x41, 0xbb, 0xe2, 0xa0, 0xb6, 0xea, 0x75, 0x66,
                    0xd2, 0xa5, 0xd1, 0xe7, 0xe2, 0x0d, 0x42, 0xaf, 0x2c, 0x53, 0xd7, 0x92, 0xb1,
                    0xc4, 0x3f, 0xea, 0x81, 0x7e, 0x9a, 0xd2, 0x75, 0xae, 0x54, 0x69, 0x63,
                ],
            },
            TestVector {
                key: [
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                ],
                nonce: [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01],
                keystream: vec![
                    0xde, 0x9c, 0xba, 0x7b, 0xf3, 0xd6, 0x9e, 0xf5, 0xe7, 0x86, 0xdc, 0x63, 0x97,
                    0x3f, 0x65, 0x3a, 0x0b, 0x49, 0xe0, 0x15, 0xad, 0xbf, 0xf7, 0x13, 0x4f, 0xcb,
                    0x7d, 0xf1, 0x37, 0x82, 0x10, 0x31, 0xe8, 0x5a, 0x05, 0x02, 0x78, 0xa7, 0x08,
                    0x45, 0x27, 0x21, 0x4f, 0x73, 0xef, 0xc7, 0xfa, 0x5b, 0x52, 0x77, 0x06, 0x2e,
                    0xb7, 0xa0, 0x43, 0x3e, 0x44, 0x5f, 0x41, 0xe3,
                ],
            },
            TestVector {
                key: [
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                ],
                nonce: [0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],
                keystream: vec![
                    0xef, 0x3f, 0xdf, 0xd6, 0xc6, 0x15, 0x78, 0xfb, 0xf5, 0xcf, 0x35, 0xbd, 0x3d,
                    0xd3, 0x3b, 0x80, 0x09, 0x63, 0x16, 0x34, 0xd2, 0x1e, 0x42, 0xac, 0x33, 0x96,
                    0x0b, 0xd1, 0x38, 0xe5, 0x0d, 0x32, 0x11, 0x1e, 0x4c, 0xaf, 0x23, 0x7e, 0xe5,
                    0x3c, 0xa8, 0xad, 0x64, 0x26, 0x19, 0x4a, 0x88, 0x54, 0x5d, 0xdc, 0x49, 0x7a,
                    0x0b, 0x46, 0x6e, 0x7d, 0x6b, 0xbd, 0xb0, 0x04, 0x1b, 0x2f, 0x58, 0x6b,
                ],
            },
            TestVector {
                key: [
                    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c,
                    0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19,
                    0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
                ],
                nonce: [0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07],
                keystream: vec![
                    0xf7, 0x98, 0xa1, 0x89, 0xf1, 0x95, 0xe6, 0x69, 0x82, 0x10, 0x5f, 0xfb, 0x64,
                    0x0b, 0xb7, 0x75, 0x7f, 0x57, 0x9d, 0xa3, 0x16, 0x02, 0xfc, 0x93, 0xec, 0x01,
                    0xac, 0x56, 0xf8, 0x5a, 0xc3, 0xc1, 0x34, 0xa4, 0x54, 0x7b, 0x73, 0x3b, 0x46,
                    0x41, 0x30, 0x42, 0xc9, 0x44, 0x00, 0x49, 0x17, 0x69, 0x05, 0xd3, 0xbe, 0x59,
                    0xea, 0x1c, 0x53, 0xf1, 0x59, 0x16, 0x15, 0x5c, 0x2b, 0xe8, 0x24, 0x1a, 0x38,
                    0x00, 0x8b, 0x9a, 0x26, 0xbc, 0x35, 0x94, 0x1e, 0x24, 0x44, 0x17, 0x7c, 0x8a,
                    0xde, 0x66, 0x89, 0xde, 0x95, 0x26, 0x49, 0x86, 0xd9, 0x58, 0x89, 0xfb, 0x60,
                    0xe8, 0x46, 0x29, 0xc9, 0xbd, 0x9a, 0x5a, 0xcb, 0x1c, 0xc1, 0x18, 0xbe, 0x56,
                    0x3e, 0xb9, 0xb3, 0xa4, 0xa4, 0x72, 0xf8, 0x2e, 0x09, 0xa7, 0xe7, 0x78, 0x49,
                    0x2b, 0x56, 0x2e, 0xf7, 0x13, 0x0e, 0x88, 0xdf, 0xe0, 0x31, 0xc7, 0x9d, 0xb9,
                    0xd4, 0xf7, 0xc7, 0xa8, 0x99, 0x15, 0x1b, 0x9a, 0x47, 0x50, 0x32, 0xb6, 0x3f,
                    0xc3, 0x85, 0x24, 0x5f, 0xe0, 0x54, 0xe3, 0xdd, 0x5a, 0x97, 0xa5, 0xf5, 0x76,
                    0xfe, 0x06, 0x40, 0x25, 0xd3, 0xce, 0x04, 0x2c, 0x56, 0x6a, 0xb2, 0xc5, 0x07,
                    0xb1, 0x38, 0xdb, 0x85, 0x3e, 0x3d, 0x69, 0x59, 0x66, 0x09, 0x96, 0x54, 0x6c,
                    0xc9, 0xc4, 0xa6, 0xea, 0xfd, 0xc7, 0x77, 0xc0, 0x40, 0xd7, 0x0e, 0xaf, 0x46,
                    0xf7, 0x6d, 0xad, 0x39, 0x79, 0xe5, 0xc5, 0x36, 0x0c, 0x33, 0x17, 0x16, 0x6a,
                    0x1c, 0x89, 0x4c, 0x94, 0xa3, 0x71, 0x87, 0x6a, 0x94, 0xdf, 0x76, 0x28, 0xfe,
                    0x4e, 0xaa, 0xf2, 0xcc, 0xb2, 0x7d, 0x5a, 0xaa, 0xe0, 0xad, 0x7a, 0xd0, 0xf9,
                    0xd4, 0xb6, 0xad, 0x3b, 0x54, 0x09, 0x87, 0x46, 0xd4, 0x52, 0x4d, 0x38, 0x40,
                    0x7a, 0x6d, 0xeb, 0x3a, 0xb7, 0x8f, 0xab, 0x78, 0xc9,
                ],
            },
        ];

        for tv in test_vectors.iter() {
            let mut c = ChaCha20::new(&tv.key, &tv.nonce);
            let input: Vec<u8> = repeat(0).take(tv.keystream.len()).collect();
            let mut output: Vec<u8> = repeat(0).take(input.len()).collect();
            c.process(&input[..], &mut output[..]);
            assert_eq!(output, tv.keystream);
        }
    }

    #[test]
    fn get_single_block() {
        // Test that `get_single_block` (which takes a 16-byte nonce) is equivalent to getting a block
        // using a 12-byte nonce, with the block starting at the counter offset given by the remaining 4
        // bytes.
        let key = [
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
            0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b,
            0x1c, 0x1d, 0x1e, 0x1f,
        ];
        let nonce_16bytes = [
            0x00, 0x01, 0x02, 0x03, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,
            0x0a, 0x0b,
        ];
        let counter_pos = &nonce_16bytes[..4];
        let nonce_12bytes = &nonce_16bytes[4..];

        // Initialize a ChaCha20 instance with its counter starting at 0.
        let mut chacha20 = ChaCha20::new(&key, nonce_12bytes);
        // Seek its counter to the block at counter_pos.
        chacha20.seek_to_block(u32::from_le_bytes(counter_pos.try_into().unwrap()));
        let mut block_bytes = [0; 32];
        chacha20.process_in_place(&mut block_bytes);

        assert_eq!(ChaCha20::get_single_block(&key, &nonce_16bytes), block_bytes);
    }
}