diff --git a/CMakeLists.txt b/CMakeLists.txt
index f143c93a..4bad0e2d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -199,6 +199,8 @@ list (
     crypto/arc4.hpp
     crypto/ice.cpp
     crypto/ice.hpp
+    crypto/salsa.cpp
+    crypto/salsa.hpp
     crypto/tea.cpp
     crypto/tea.hpp
     crypto/xtea.cpp
@@ -456,6 +458,7 @@ if (TESTS)
         coord
         crypto/arc4
         crypto/ice
+        crypto/salsa
         crypto/tea
         crypto/xtea
         crypto/xxtea
diff --git a/crypto/salsa.cpp b/crypto/salsa.cpp
new file mode 100644
index 00000000..2cf5590b
--- /dev/null
+++ b/crypto/salsa.cpp
@@ -0,0 +1,24 @@
+#include "./salsa.hpp"
+
+
+///////////////////////////////////////////////////////////////////////////////
+std::array<uint8_t,64>
+util::crypto::salsa20 (const std::array<uint8_t,64> bytes) noexcept
+{
+    auto x = *reinterpret_cast<const std::array<uint32_t,16>*> (&bytes);
+    auto y = x;
+
+    for (auto &t: x)
+        t = util::ltoh (t);
+
+    for (int i = 0; i < 10; ++i)
+        x = salsa::doubleround (x);
+
+    for (size_t i = 0; i < std::size (y); ++i)
+        x[i] += y[i];
+
+    for (auto &t: x)
+        t = util::htol (t);
+
+    return *reinterpret_cast<std::array<uint8_t,64>*> (&x);
+}
diff --git a/crypto/salsa.hpp b/crypto/salsa.hpp
new file mode 100644
index 00000000..c8d81c64
--- /dev/null
+++ b/crypto/salsa.hpp
@@ -0,0 +1,86 @@
+#include <cstdint>
+#include <array>
+
+#include "../bitwise.hpp"
+#include "../endian.hpp"
+
+namespace util::crypto::salsa {
+
+    ///////////////////////////////////////////////////////////////////////////
+    constexpr
+    uint32_t
+    R (uint32_t a, uint32_t b, uint32_t c, uint32_t k)
+    {
+        return b ^ util::rotatel (a + c, k);
+    }
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    constexpr
+    std::array<uint32_t,4>
+    quarter (std::array<uint32_t,4> y) noexcept
+    {
+        std::array<uint32_t,4> z {};
+
+        z[1] = R (y[0], y[1], y[3],  7);
+        z[2] = R (z[1], y[2], y[0],  9);
+        z[3] = R (z[2], y[3], z[1], 13);
+        z[0] = R (z[3], y[0], z[2], 18);
+
+        return z;
+    }
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    constexpr
+    std::array<uint32_t,16>
+    row (const std::array<uint32_t,16> y) noexcept
+    {
+        const auto [z00, z01, z02, z03] = quarter ({y[ 0], y[ 1], y[ 2], y[ 3]});
+        const auto [z05, z06, z07, z04] = quarter ({y[ 5], y[ 6], y[ 7], y[ 4]});
+        const auto [z10, z11, z08, z09] = quarter ({y[10], y[11], y[ 8], y[ 9]});
+        const auto [z15, z12, z13, z14] = quarter ({y[15], y[12], y[13], y[14]});
+
+        return {
+            z00, z01, z02, z03,
+            z04, z05, z06, z07,
+            z08, z09, z10, z11,
+            z12, z13, z14, z15
+        };
+    }
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    constexpr
+    std::array<uint32_t,16>
+    col (const std::array<uint32_t,16> x) noexcept
+    {
+        const auto [y00, y04, y08, y12] = quarter ({x[ 0], x[ 4], x[ 8], x[12]});
+        const auto [y05, y09, y13, y01] = quarter ({x[ 5], x[ 9], x[13], x[ 1]});
+        const auto [y10, y14, y02, y06] = quarter ({x[10], x[14], x[ 2], x[ 6]});
+        const auto [y15, y03, y07, y11] = quarter ({x[15], x[ 3], x[ 7], x[11]});
+
+        return {
+            y00, y01, y02, y03,
+            y04, y05, y06, y07,
+            y08, y09, y10, y11,
+            y12, y13, y14, y15,
+        };
+    }
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    constexpr
+    std::array<uint32_t,16>
+    doubleround (const std::array<uint32_t,16> x) noexcept
+    {
+        return row (col (x));
+    }
+}
+
+
+namespace util::crypto {
+    ///////////////////////////////////////////////////////////////////////////
+    std::array<uint8_t,64>
+    salsa20 (const std::array<uint8_t,64>) noexcept;
+}
diff --git a/test/crypto/salsa.cpp b/test/crypto/salsa.cpp
new file mode 100644
index 00000000..e3478be9
--- /dev/null
+++ b/test/crypto/salsa.cpp
@@ -0,0 +1,229 @@
+#include "crypto/salsa.hpp"
+
+#include "tap.hpp"
+
+
+///////////////////////////////////////////////////////////////////////////////
+void
+test_quarter (util::TAP::logger &tap)
+{
+    static const struct {
+        std::array<uint32_t, 4> a, b;
+    } TESTS[] = {
+        { { 0x00000000, 0x00000000, 0x00000000, 0x00000000 },
+          { 0x00000000, 0x00000000, 0x00000000, 0x00000000 } },
+        { { 0x00000001, 0x00000000, 0x00000000, 0x00000000 },
+          { 0x08008145, 0x00000080, 0x00010200, 0x20500000 } },
+        { { 0x00000000, 0x00000001, 0x00000000, 0x00000000 },
+          { 0x88000100, 0x00000001, 0x00000200, 0x00402000 } },
+        { { 0x00000000, 0x00000000, 0x00000001, 0x00000000 },
+          { 0x80040000, 0x00000000, 0x00000001, 0x00002000 } },
+        { { 0x00000000, 0x00000000, 0x00000000, 0x00000001 },
+          { 0x00048044, 0x00000080, 0x00010000, 0x20100001 } },
+        { { 0xe7e8c006, 0xc4f9417d, 0x6479b4b2, 0x68c67137 },
+          { 0xe876d72b, 0x9361dfd5, 0xf1460244, 0x948541a3 } },
+        { { 0xd3917c5b, 0x55f1c407, 0x52a58a7a, 0x8f887a3b },
+          { 0x3e2f308c, 0xd90a8f36, 0x6ab2a923, 0x2883524c } },
+    };
+
+    for (size_t i = 0; i < std::size (TESTS); ++i)
+        tap.expect_eq (util::crypto::salsa::quarter (TESTS[i].a), TESTS[i].b, "quarter %zu", i);
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+void
+test_row (util::TAP::logger &tap)
+{
+    static const struct {
+        std::array<uint32_t, 16> a, b;
+    } TESTS[] = {
+        { { 0x00000001, 0x00000000, 0x00000000, 0x00000000,
+            0x00000001, 0x00000000, 0x00000000, 0x00000000,
+            0x00000001, 0x00000000, 0x00000000, 0x00000000,
+            0x00000001, 0x00000000, 0x00000000, 0x00000000, },
+          { 0x08008145, 0x00000080, 0x00010200, 0x20500000,
+            0x20100001, 0x00048044, 0x00000080, 0x00010000,
+            0x00000001, 0x00002000, 0x80040000, 0x00000000,
+            0x00000001, 0x00000200, 0x00402000, 0x88000100, }
+        },
+        { { 0x08521bd6, 0x1fe88837, 0xbb2aa576, 0x3aa26365,
+            0xc54c6a5b, 0x2fc74c2f, 0x6dd39cc3, 0xda0a64f6,
+            0x90a2f23d, 0x067f95a6, 0x06b35f61, 0x41e4732e,
+            0xe859c100, 0xea4d84b7, 0x0f619bff, 0xbc6e965a, },
+          { 0xa890d39d, 0x65d71596, 0xe9487daa, 0xc8ca6a86,
+            0x949d2192, 0x764b7754, 0xe408d9b9, 0x7a41b4d1,
+            0x3402e183, 0x3c3af432, 0x50669f96, 0xd89ef0a8,
+            0x0040ede5, 0xb545fbce, 0xd257ed4f, 0x1818882d, },
+        }
+    };
+
+    for (size_t i = 0; i < std::size (TESTS); ++i)
+        tap.expect_eq (util::crypto::salsa::row (TESTS[i].a), TESTS[i].b, "row %zu", i);
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+void
+test_col (util::TAP::logger &tap)
+{
+    static const struct {
+        std::array<uint32_t,16> a, b;
+    } TESTS[] = {
+        { { 0x00000001, 0x00000000, 0x00000000, 0x00000000,
+            0x00000001, 0x00000000, 0x00000000, 0x00000000,
+            0x00000001, 0x00000000, 0x00000000, 0x00000000,
+            0x00000001, 0x00000000, 0x00000000, 0x00000000, },
+          { 0x10090288, 0x00000000, 0x00000000, 0x00000000,
+            0x00000101, 0x00000000, 0x00000000, 0x00000000,
+            0x00020401, 0x00000000, 0x00000000, 0x00000000,
+            0x40a04001, 0x00000000, 0x00000000, 0x00000000, } },
+        { { 0x08521bd6, 0x1fe88837, 0xbb2aa576, 0x3aa26365,
+            0xc54c6a5b, 0x2fc74c2f, 0x6dd39cc3, 0xda0a64f6,
+            0x90a2f23d, 0x067f95a6, 0x06b35f61, 0x41e4732e,
+            0xe859c100, 0xea4d84b7, 0x0f619bff, 0xbc6e965a, },
+          { 0x8c9d190a, 0xce8e4c90, 0x1ef8e9d3, 0x1326a71a,
+            0x90a20123, 0xead3c4f3, 0x63a091a0, 0xf0708d69,
+            0x789b010c, 0xd195a681, 0xeb7d5504, 0xa774135c,
+            0x481c2027, 0x53a8e4b5, 0x4c1f89c5, 0x3f78c9c8, } },
+    };
+
+    for (size_t i = 0; i < std::size (TESTS); ++i)
+        tap.expect_eq (util::crypto::salsa::col (TESTS[i].a), TESTS[i].b, "col %zu", i);
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+void
+test_doubleround (util::TAP::logger &tap)
+{
+    static const struct {
+        std::array<uint32_t,16> a, b;
+    } TESTS[] = {
+        { { 0x00000001, 0x00000000, 0x00000000, 0x00000000,
+            0x00000000, 0x00000000, 0x00000000, 0x00000000,
+            0x00000000, 0x00000000, 0x00000000, 0x00000000,
+            0x00000000, 0x00000000, 0x00000000, 0x00000000, },
+          { 0x8186a22d, 0x0040a284, 0x82479210, 0x06929051,
+            0x08000090, 0x02402200, 0x00004000, 0x00800000,
+            0x00010200, 0x20400000, 0x08008104, 0x00000000,
+            0x20500000, 0xa0000040, 0x0008180a, 0x612a8020, } },
+        { { 0xde501066, 0x6f9eb8f7, 0xe4fbbd9b, 0x454e3f57,
+            0xb75540d3, 0x43e93a4c, 0x3a6f2aa0, 0x726d6b36,
+            0x9243f484, 0x9145d1e8, 0x4fa9d247, 0xdc8dee11,
+            0x054bf545, 0x254dd653, 0xd9421b6d, 0x67b276c1, },
+          { 0xccaaf672, 0x23d960f7, 0x9153e63a, 0xcd9a60d0,
+            0x50440492, 0xf07cad19, 0xae344aa0, 0xdf4cfdfc,
+            0xca531c29, 0x8e7943db, 0xac1680cd, 0xd503ca00,
+            0xa74b2ad6, 0xbc331c5c, 0x1dda24c7, 0xee928277, } }
+    };
+
+    for (size_t i = 0; i < std::size (TESTS); ++i)
+        tap.expect_eq (util::crypto::salsa::doubleround (TESTS[i].a), TESTS[i].b, "doubleround %zu", i);
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+void
+test_salsa20 (util::TAP::logger &tap)
+{
+    static const struct {
+        std::array<uint8_t,64> a, b;
+    } TESTS[] = {
+        { { 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,
+            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 },
+          { 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,
+            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 } },
+
+        { { 0xd3, 0x9f, 0x0d, 0x73, 0x4c, 0x37, 0x52, 0xb7,
+            0x03, 0x75, 0xde, 0x25, 0xbf, 0xbb, 0xea, 0x88,
+            0x31, 0xed, 0xb3, 0x30, 0x01, 0x6a, 0xb2, 0xdb,
+            0xaf, 0xc7, 0xa6, 0x30, 0x56, 0x10, 0xb3, 0xcf,
+            0x1f, 0xf0, 0x20, 0x3f, 0x0f, 0x53, 0x5d, 0xa1,
+            0x74, 0x93, 0x30, 0x71, 0xee, 0x37, 0xcc, 0x24,
+            0x4f, 0xc9, 0xeb, 0x4f, 0x03, 0x51, 0x9c, 0x2f,
+            0xcb, 0x1a, 0xf4, 0xf3, 0x58, 0x76, 0x68, 0x36 },
+          { 0x6d, 0x2a, 0xb2, 0xa8, 0x9c, 0xf0, 0xf8, 0xee,
+            0xa8, 0xc4, 0xbe, 0xcb, 0x1a, 0x6e, 0xaa, 0x9a,
+            0x1d, 0x1d, 0x96, 0x1a, 0x96, 0x1e, 0xeb, 0xf9,
+            0xbe, 0xa3, 0xfb, 0x30, 0x45, 0x90, 0x33, 0x39,
+            0x76, 0x28, 0x98, 0x9d, 0xb4, 0x39, 0x1b, 0x5e,
+            0x6b, 0x2a, 0xec, 0x23, 0x1b, 0x6f, 0x72, 0x72,
+            0xdb, 0xec, 0xe8, 0x87, 0x6f, 0x9b, 0x6e, 0x12,
+            0x18, 0xe8, 0x5f, 0x9e, 0xb3, 0x13, 0x30, 0xca } },
+
+        { { 0x58, 0x76, 0x68, 0x36, 0x4f, 0xc9, 0xeb, 0x4f,
+            0x03, 0x51, 0x9c, 0x2f, 0xcb, 0x1a, 0xf4, 0xf3,
+            0xbf, 0xbb, 0xea, 0x88, 0xd3, 0x9f, 0x0d, 0x73,
+            0x4c, 0x37, 0x52, 0xb7, 0x03, 0x75, 0xde, 0x25,
+            0x56, 0x10, 0xb3, 0xcf, 0x31, 0xed, 0xb3, 0x30,
+            0x01, 0x6a, 0xb2, 0xdb, 0xaf, 0xc7, 0xa6, 0x30,
+            0xee, 0x37, 0xcc, 0x24, 0x1f, 0xf0, 0x20, 0x3f,
+            0x0f, 0x53, 0x5d, 0xa1, 0x74, 0x93, 0x30, 0x71 },
+          { 0xb3, 0x13, 0x30, 0xca, 0xdb, 0xec, 0xe8, 0x87,
+            0x6f, 0x9b, 0x6e, 0x12, 0x18, 0xe8, 0x5f, 0x9e,
+            0x1a, 0x6e, 0xaa, 0x9a, 0x6d, 0x2a, 0xb2, 0xa8,
+            0x9c, 0xf0, 0xf8, 0xee, 0xa8, 0xc4, 0xbe, 0xcb,
+            0x45, 0x90, 0x33, 0x39, 0x1d, 0x1d, 0x96, 0x1a,
+            0x96, 0x1e, 0xeb, 0xf9, 0xbe, 0xa3, 0xfb, 0x30,
+            0x1b, 0x6f, 0x72, 0x72, 0x76, 0x28, 0x98, 0x9d,
+            0xb4, 0x39, 0x1b, 0x5e, 0x6b, 0x2a, 0xec, 0x23 } }
+    };
+
+    for (size_t i = 0; i < std::size (TESTS); ++i)
+        tap.expect_eq (util::crypto::salsa20 (TESTS[i].a), TESTS[i].b, "salsa20 %zu", i);
+
+    struct {
+        std::array<uint8_t,64> a, b;
+    } million = {
+        { 0x06, 0x7c, 0x53, 0x92, 0x26, 0xbf, 0x09, 0x32,
+          0x04, 0xa1, 0x2f, 0xde, 0x7a, 0xb6, 0xdf, 0xb9,
+          0x4b, 0x1b, 0x00, 0xd8, 0x10, 0x7a, 0x07, 0x59,
+          0xa2, 0x68, 0x65, 0x93, 0xd5, 0x15, 0x36, 0x5f,
+          0xe1, 0xfd, 0x8b, 0xb0, 0x69, 0x84, 0x17, 0x74,
+          0x4c, 0x29, 0xb0, 0xcf, 0xdd, 0x22, 0x9d, 0x6c,
+          0x5e, 0x5e, 0x63, 0x34, 0x5a, 0x75, 0x5b, 0xdc,
+          0x92, 0xbe, 0xef, 0x8f, 0xc4, 0xb0, 0x82, 0xba },
+        { 0x08, 0x12, 0x26, 0xc7, 0x77, 0x4c, 0xd7, 0x43,
+          0xad, 0x7f, 0x90, 0xa2, 0x67, 0xd4, 0xb0, 0xd9,
+          0xc0, 0x13, 0xe9, 0x21, 0x9f, 0xc5, 0x9a, 0xa0,
+          0x80, 0xf3, 0xdb, 0x41, 0xab, 0x88, 0x87, 0xe1,
+          0x7b, 0x0b, 0x44, 0x56, 0xed, 0x52, 0x14, 0x9b,
+          0x85, 0xbd, 0x09, 0x53, 0xa7, 0x74, 0xc2, 0x4e,
+          0x7a, 0x7f, 0xc3, 0xb9, 0xb9, 0xcc, 0xbc, 0x5a,
+          0xf5, 0x09, 0xb7, 0xf8, 0xe2, 0x55, 0xf5, 0x68 }
+    };
+
+    for (int i = 0; i < 1'000'000; ++i)
+        million.a = util::crypto::salsa20 (million.a);
+
+    tap.expect_eq (million.a, million.b, "salsa20 million");
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+int
+main (void)
+{
+    util::TAP::logger tap;
+
+    test_quarter (tap);
+    test_row (tap);
+    test_col (tap);
+    test_doubleround (tap);
+    test_salsa20 (tap);
+
+    return 0;
+}