diff --git a/chacha20/src/block.rs b/chacha20/src/block/mod.rs
similarity index 98%
rename from chacha20/src/block.rs
rename to chacha20/src/block/mod.rs
index 989a0f8c..daa9956e 100644
--- a/chacha20/src/block.rs
+++ b/chacha20/src/block/mod.rs
@@ -4,6 +4,9 @@
 
 use salsa20_core::{CONSTANTS, IV_WORDS, KEY_WORDS, STATE_WORDS};
 
+#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+pub(crate) mod sse2;
+
 /// The ChaCha20 block function
 ///
 /// While ChaCha20 is a stream cipher, not a block cipher, its core
diff --git a/chacha20/src/block/sse2.rs b/chacha20/src/block/sse2.rs
new file mode 100644
index 00000000..e2a7dd3a
--- /dev/null
+++ b/chacha20/src/block/sse2.rs
@@ -0,0 +1,236 @@
+#[cfg(target_arch = "x86")]
+use core::arch::x86::*;
+#[cfg(target_arch = "x86_64")]
+use core::arch::x86_64::*;
+
+use salsa20_core::{CONSTANTS, IV_WORDS, KEY_WORDS, STATE_WORDS};
+
+pub(crate) struct Block {
+    v0: __m128i,
+    v1: __m128i,
+    v2: __m128i,
+    v3: __m128i,
+}
+
+impl Block {
+    #[target_feature(enable = "sse2")]
+    pub(crate) unsafe fn generate(
+        key: &[u32; KEY_WORDS],
+        iv: [u32; IV_WORDS],
+        counter: u64,
+    ) -> [u32; STATE_WORDS] {
+        let vs = init(key, iv, counter);
+
+        let mut block = Self {
+            v0: vs[0],
+            v1: vs[1],
+            v2: vs[2],
+            v3: vs[3],
+        };
+
+        block.rounds();
+        block.finish(key, iv, counter)
+    }
+
+    #[inline]
+    #[target_feature(enable = "sse2")]
+    pub unsafe fn rounds(&mut self) {
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+        double_quarter_round(&mut self.v0, &mut self.v1, &mut self.v2, &mut self.v3);
+    }
+
+    #[inline]
+    #[target_feature(enable = "sse2")]
+    unsafe fn finish(
+        mut self,
+        key: &[u32; KEY_WORDS],
+        iv: [u32; IV_WORDS],
+        counter: u64,
+    ) -> [u32; STATE_WORDS] {
+        let vs = init(key, iv, counter);
+
+        self.v0 = _mm_add_epi32(self.v0, vs[0]);
+        self.v1 = _mm_add_epi32(self.v1, vs[1]);
+        self.v2 = _mm_add_epi32(self.v2, vs[2]);
+        self.v3 = _mm_add_epi32(self.v3, vs[3]);
+
+        store(self.v0, self.v1, self.v2, self.v3)
+    }
+}
+
+#[inline]
+#[target_feature(enable = "sse2")]
+unsafe fn init(key: &[u32; KEY_WORDS], iv: [u32; IV_WORDS], counter: u64) -> [__m128i; 4] {
+    let v0 = _mm_loadu_si128(CONSTANTS.as_ptr() as *const __m128i);
+    let v1 = _mm_loadu_si128(key.as_ptr().offset(0) as *const __m128i);
+    let v2 = _mm_loadu_si128(key.as_ptr().offset(4) as *const __m128i);
+    let v3 = _mm_set_epi32(
+        iv[1] as i32,
+        iv[0] as i32,
+        ((counter >> 32) & 0xffff_ffff) as i32,
+        (counter & 0xffff_ffff) as i32,
+    );
+
+    [v0, v1, v2, v3]
+}
+
+#[inline]
+#[target_feature(enable = "sse2")]
+unsafe fn store(v0: __m128i, v1: __m128i, v2: __m128i, v3: __m128i) -> [u32; STATE_WORDS] {
+    let mut state = [0u32; STATE_WORDS];
+
+    _mm_storeu_si128(state.as_mut_ptr().offset(0x0) as *mut __m128i, v0);
+    _mm_storeu_si128(state.as_mut_ptr().offset(0x4) as *mut __m128i, v1);
+    _mm_storeu_si128(state.as_mut_ptr().offset(0x8) as *mut __m128i, v2);
+    _mm_storeu_si128(state.as_mut_ptr().offset(0xc) as *mut __m128i, v3);
+
+    state
+}
+
+#[inline]
+#[target_feature(enable = "sse2")]
+unsafe fn double_quarter_round(
+    v0: &mut __m128i,
+    v1: &mut __m128i,
+    v2: &mut __m128i,
+    v3: &mut __m128i,
+) {
+    add_xor_rot(v0, v1, v2, v3);
+    rows_to_cols(v0, v1, v2, v3);
+    add_xor_rot(v0, v1, v2, v3);
+    cols_to_rows(v0, v1, v2, v3);
+}
+
+#[inline]
+#[target_feature(enable = "sse2")]
+unsafe fn rows_to_cols(_v0: &mut __m128i, v1: &mut __m128i, v2: &mut __m128i, v3: &mut __m128i) {
+    // v1 >>>= 32; v2 >>>= 64; v3 >>>= 96;
+    *v1 = _mm_shuffle_epi32(*v1, 0b_00_11_10_01); // _MM_SHUFFLE(0, 3, 2, 1)
+    *v2 = _mm_shuffle_epi32(*v2, 0b_01_00_11_10); // _MM_SHUFFLE(1, 0, 3, 2)
+    *v3 = _mm_shuffle_epi32(*v3, 0b_10_01_00_11); // _MM_SHUFFLE(2, 1, 0, 3)
+}
+
+#[inline]
+#[target_feature(enable = "sse2")]
+unsafe fn cols_to_rows(_v0: &mut __m128i, v1: &mut __m128i, v2: &mut __m128i, v3: &mut __m128i) {
+    // v1 <<<= 32; v2 <<<= 64; v3 <<<= 96;
+    *v1 = _mm_shuffle_epi32(*v1, 0b_10_01_00_11); // _MM_SHUFFLE(2, 1, 0, 3)
+    *v2 = _mm_shuffle_epi32(*v2, 0b_01_00_11_10); // _MM_SHUFFLE(1, 0, 3, 2)
+    *v3 = _mm_shuffle_epi32(*v3, 0b_00_11_10_01); // _MM_SHUFFLE(0, 3, 2, 1)
+}
+
+#[inline]
+#[target_feature(enable = "sse2")]
+unsafe fn add_xor_rot(v0: &mut __m128i, v1: &mut __m128i, v2: &mut __m128i, v3: &mut __m128i) {
+    // v0 += v1; v3 ^= v0; v3 <<<= (16, 16, 16, 16);
+    *v0 = _mm_add_epi32(*v0, *v1);
+    *v3 = _mm_xor_si128(*v3, *v0);
+    *v3 = _mm_xor_si128(_mm_slli_epi32(*v3, 16), _mm_srli_epi32(*v3, 16));
+
+    // v2 += v3; v1 ^= v2; v1 <<<= (12, 12, 12, 12);
+    *v2 = _mm_add_epi32(*v2, *v3);
+    *v1 = _mm_xor_si128(*v1, *v2);
+    *v1 = _mm_xor_si128(_mm_slli_epi32(*v1, 12), _mm_srli_epi32(*v1, 20));
+
+    // v0 += v1; v3 ^= v0; v3 <<<= (8, 8, 8, 8);
+    *v0 = _mm_add_epi32(*v0, *v1);
+    *v3 = _mm_xor_si128(*v3, *v0);
+    *v3 = _mm_xor_si128(_mm_slli_epi32(*v3, 8), _mm_srli_epi32(*v3, 24));
+
+    // v2 += v3; v1 ^= v2; v1 <<<= (7, 7, 7, 7);
+    *v2 = _mm_add_epi32(*v2, *v3);
+    *v1 = _mm_xor_si128(*v1, *v2);
+    *v1 = _mm_xor_si128(_mm_slli_epi32(*v1, 7), _mm_srli_epi32(*v1, 25));
+}
+
+#[cfg(all(test, target_feature = "sse2"))]
+mod tests {
+    use super::super::Block as ScalarBlock;
+    use super::*;
+
+    // random inputs for testing
+    const R_CNT: u64 = 0x9fe625b6d23a8fa8u64;
+    const R_IV: [u32; IV_WORDS] = [0x4aa8962f, 0x94bc92f8];
+    const R_KEY: [u32; KEY_WORDS] = [
+        0x9972f211, 0xef6d79e1, 0x586adc0b, 0x9458011f, 0x3f691992, 0x721635e9, 0x940dd163,
+        0x1134316d,
+    ];
+
+    #[test]
+    fn init_and_store() {
+        unsafe {
+            let vs = init(&R_KEY, R_IV, R_CNT);
+            let state = store(vs[0], vs[1], vs[2], vs[3]);
+
+            assert_eq!(
+                state.as_ref(),
+                &[
+                    1634760805, 857760878, 2036477234, 1797285236, 2574447121, 4016929249,
+                    1483398155, 2488795423, 1063852434, 1914058217, 2483933539, 288633197,
+                    3527053224, 2682660278, 1252562479, 2495386360
+                ]
+            );
+        }
+    }
+
+    #[test]
+    fn init_and_finish() {
+        unsafe {
+            let vs = init(&R_KEY, R_IV, R_CNT);
+            let block = Block {
+                v0: vs[0],
+                v1: vs[1],
+                v2: vs[2],
+                v3: vs[3],
+            };
+
+            assert_eq!(
+                block.finish(&R_KEY, R_IV, R_CNT).as_ref(),
+                &[
+                    3269521610, 1715521756, 4072954468, 3594570472, 853926946, 3738891202,
+                    2966796310, 682623550, 2127704868, 3828116434, 672899782, 577266394,
+                    2759139152, 1070353260, 2505124958, 695805424
+                ]
+            );
+        }
+    }
+
+    #[test]
+    fn init_and_double_round() {
+        unsafe {
+            let vs = init(&R_KEY, R_IV, R_CNT);
+            let mut v0 = vs[0];
+            let mut v1 = vs[1];
+            let mut v2 = vs[2];
+            let mut v3 = vs[3];
+            double_quarter_round(&mut v0, &mut v1, &mut v2, &mut v3);
+            let state = store(v0, v1, v2, v3);
+
+            assert_eq!(
+                state.as_ref(),
+                &[
+                    562456049, 3130322832, 1534507163, 1938142593, 1427879055, 3727017100,
+                    1549525649, 2358041203, 1010155040, 657444539, 2865892668, 2826477124,
+                    737507996, 3254278724, 3376929372, 928763221
+                ]
+            );
+        }
+    }
+
+    #[test]
+    fn generate_vs_scalar_impl() {
+        let scalar_result = ScalarBlock::generate(&R_KEY, R_IV, R_CNT);
+        let simd_result = unsafe { Block::generate(&R_KEY, R_IV, R_CNT) };
+
+        assert_eq!(scalar_result, simd_result)
+    }
+}
diff --git a/chacha20/src/cipher.rs b/chacha20/src/cipher.rs
index 97d58a23..131efd43 100644
--- a/chacha20/src/cipher.rs
+++ b/chacha20/src/cipher.rs
@@ -1,6 +1,5 @@
 //! ChaCha20 cipher core implementation
 
-use block::Block;
 use byteorder::{ByteOrder, LE};
 use salsa20_core::{SalsaFamilyCipher, IV_WORDS, KEY_WORDS, STATE_WORDS};
 
@@ -42,7 +41,24 @@ impl Cipher {
 
 impl SalsaFamilyCipher for Cipher {
     #[inline]
+    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     fn block(&self, counter: u64) -> [u32; STATE_WORDS] {
-        Block::generate(&self.key, self.iv, self.counter_offset + counter)
+        if cfg!(target_feature = "sse2") {
+            unsafe {
+                super::block::sse2::Block::generate(
+                    &self.key,
+                    self.iv,
+                    self.counter_offset + counter,
+                )
+            }
+        } else {
+            super::block::Block::generate(&self.key, self.iv, self.counter_offset + counter)
+        }
+    }
+
+    #[inline]
+    #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
+    fn block(&self, counter: u64) -> [u32; STATE_WORDS] {
+        super::block::Block::generate(&self.key, self.iv, self.counter_offset + counter)
     }
 }