diff --git a/block/rc2.cpp b/block/rc2.cpp
index 1f378fa..666d467 100644
--- a/block/rc2.cpp
+++ b/block/rc2.cpp
@@ -8,6 +8,136 @@
 
 #include "rc2.hpp"
 
+#include <cruft/util/bitwise.hpp>
+#include <cruft/util/endian.hpp>
+
+using cruft::crypto::block::rc2;
+
 
 ///////////////////////////////////////////////////////////////////////////////
+static constexpr std::array<u08,256> PITABLE {
+    0xd9, 0x78, 0xf9, 0xc4, 0x19, 0xdd, 0xb5, 0xed, 0x28, 0xe9, 0xfd, 0x79, 0x4a, 0xa0, 0xd8, 0x9d,
+    0xc6, 0x7e, 0x37, 0x83, 0x2b, 0x76, 0x53, 0x8e, 0x62, 0x4c, 0x64, 0x88, 0x44, 0x8b, 0xfb, 0xa2,
+    0x17, 0x9a, 0x59, 0xf5, 0x87, 0xb3, 0x4f, 0x13, 0x61, 0x45, 0x6d, 0x8d, 0x09, 0x81, 0x7d, 0x32,
+    0xbd, 0x8f, 0x40, 0xeb, 0x86, 0xb7, 0x7b, 0x0b, 0xf0, 0x95, 0x21, 0x22, 0x5c, 0x6b, 0x4e, 0x82,
+    0x54, 0xd6, 0x65, 0x93, 0xce, 0x60, 0xb2, 0x1c, 0x73, 0x56, 0xc0, 0x14, 0xa7, 0x8c, 0xf1, 0xdc,
+    0x12, 0x75, 0xca, 0x1f, 0x3b, 0xbe, 0xe4, 0xd1, 0x42, 0x3d, 0xd4, 0x30, 0xa3, 0x3c, 0xb6, 0x26,
+    0x6f, 0xbf, 0x0e, 0xda, 0x46, 0x69, 0x07, 0x57, 0x27, 0xf2, 0x1d, 0x9b, 0xbc, 0x94, 0x43, 0x03,
+    0xf8, 0x11, 0xc7, 0xf6, 0x90, 0xef, 0x3e, 0xe7, 0x06, 0xc3, 0xd5, 0x2f, 0xc8, 0x66, 0x1e, 0xd7,
+    0x08, 0xe8, 0xea, 0xde, 0x80, 0x52, 0xee, 0xf7, 0x84, 0xaa, 0x72, 0xac, 0x35, 0x4d, 0x6a, 0x2a,
+    0x96, 0x1a, 0xd2, 0x71, 0x5a, 0x15, 0x49, 0x74, 0x4b, 0x9f, 0xd0, 0x5e, 0x04, 0x18, 0xa4, 0xec,
+    0xc2, 0xe0, 0x41, 0x6e, 0x0f, 0x51, 0xcb, 0xcc, 0x24, 0x91, 0xaf, 0x50, 0xa1, 0xf4, 0x70, 0x39,
+    0x99, 0x7c, 0x3a, 0x85, 0x23, 0xb8, 0xb4, 0x7a, 0xfc, 0x02, 0x36, 0x5b, 0x25, 0x55, 0x97, 0x31,
+    0x2d, 0x5d, 0xfa, 0x98, 0xe3, 0x8a, 0x92, 0xae, 0x05, 0xdf, 0x29, 0x10, 0x67, 0x6c, 0xba, 0xc9,
+    0xd3, 0x00, 0xe6, 0xcf, 0xe1, 0x9e, 0xa8, 0x2c, 0x63, 0x16, 0x01, 0x3f, 0x58, 0xe2, 0x89, 0xa9,
+    0x0d, 0x38, 0x34, 0x1b, 0xab, 0x33, 0xff, 0xb0, 0xbb, 0x48, 0x0c, 0x5f, 0xb9, 0xb1, 0xcd, 0x2e,
+    0xc5, 0xf3, 0xdb, 0x47, 0xe5, 0xa5, 0x9c, 0x77, 0x0a, 0xa6, 0x20, 0x68, 0xfe, 0x7f, 0xc1, 0xad,
+};
 
+
+///////////////////////////////////////////////////////////////////////////////
+rc2::rc2 (
+    cruft::view<u08 const*> const key,
+    int const effective_bits
+) {
+    // Ensure we don't exceed maximum key or effective lengths.
+    if (auto len = key.size (); len > 128 || len <= 0)
+        throw std::invalid_argument ("invalid key size");
+    if (effective_bits > 1024)
+        throw std::invalid_argument ("invalid effective key size");
+
+    // Copy the initial raw key bytes into the key area
+    auto xkb = cruft::make_byte_view<u08> (m_key);
+    std::copy (key.begin (), key.end (), xkb.begin ());
+
+    // Mix bytes from Pi into the remaining region
+    if (auto len = key.size (); len < 128) {
+        int i = 0;
+
+        for (u08 x = key[len - 1]; len < 128; ++len) {
+            x += xkb[i++];
+            x &= 0xff;
+            x  = PITABLE[x];
+
+            xkb[len] = x;
+        }
+    }
+
+    // Reduce the 'effective' bits of the key
+    auto const effective_bytes = cruft::divup (effective_bits, 8);
+    int remain = 128 - effective_bytes;
+    u08 const mask = 0xff >> (8 * effective_bytes - effective_bits);
+
+    u08 x = xkb[remain] & mask;
+    x = PITABLE[x];
+    xkb[remain] = x;
+
+    while (remain--) {
+        x ^= xkb[remain + effective_bytes];
+        x  = PITABLE[x];
+
+        xkb[remain] = x;
+    }
+
+    // Convert to little endian for output
+    for (auto &k: m_key)
+        k = cruft::htol (k);
+}
+
+
+//-----------------------------------------------------------------------------
+rc2::rc2 (cruft::view<u08 const *> key)
+    : rc2 (key, 1024)
+{ ; }
+
+
+///////////////////////////////////////////////////////////////////////////////
+std::array<u16,4>
+rc2::encrypt (std::array<u16,4> src) const noexcept
+{
+    auto [r0, r1, r2, r3] = src;
+
+    for (int i = 0; i < 16; i++) {
+        auto const offset = 4 * i;
+
+        r0 += m_key[offset + 0] + (r3 & r2) + (~r3 & r1); r0  = cruft::rotatel (r0, 1);
+        r1 += m_key[offset + 1] + (r0 & r3) + (~r0 & r2); r1  = cruft::rotatel (r1, 2);
+        r2 += m_key[offset + 2] + (r1 & r0) + (~r1 & r3); r2  = cruft::rotatel (r2, 3);
+        r3 += m_key[offset + 3] + (r2 & r1) + (~r2 & r0); r3  = cruft::rotatel (r3, 5);
+
+        if (i == 4 || i == 10) {
+            r0 += m_key[r3 & 63];
+            r1 += m_key[r0 & 63];
+            r2 += m_key[r1 & 63];
+            r3 += m_key[r2 & 63];
+        }
+    }
+
+    return { r0, r1, r2, r3 };
+}
+
+
+//-----------------------------------------------------------------------------
+std::array<u16,4>
+rc2::decrypt (std::array<u16,4> src) const noexcept
+{
+    auto [r0,r1,r2,r3] = src;
+
+    for (int i = 15; i >= 0; --i) {
+        auto const offset = 4 * i;
+
+        r3  = cruft::rotatel (r3, 11); r3 -= m_key[offset + 3] + (r2 & r1) + (~r2 & r0);
+        r2  = cruft::rotatel (r2, 13); r2 -= m_key[offset + 2] + (r1 & r0) + (~r1 & r3);
+        r1  = cruft::rotatel (r1, 14); r1 -= m_key[offset + 1] + (r0 & r3) + (~r0 & r2);
+        r0  = cruft::rotatel (r0, 15); r0 -= m_key[offset + 0] + (r3 & r2) + (~r3 & r1);
+
+        if (i == 5 || i == 11) {
+            r3 -= m_key[r2 & 63];
+            r2 -= m_key[r1 & 63];
+            r1 -= m_key[r0 & 63];
+            r0 -= m_key[r3 & 63];
+        }
+    }
+
+    return { r0, r1, r2, r3 };
+}
\ No newline at end of file
diff --git a/block/rc2.hpp b/block/rc2.hpp
index 21c878c..c31c61d 100644
--- a/block/rc2.hpp
+++ b/block/rc2.hpp
@@ -19,12 +19,13 @@ namespace cruft::crypto::block {
     class rc2 {
     public:
         using word_t = u16;
-        static constexpr auto block_size = sizeof (word_t) * 4;
+        using block_t = std::array<word_t,4>;
 
-        explicit rc2 (cruft::view<u16 const*> key);
+        explicit rc2 (cruft::view<u08 const*> key, int effective_bits);
+        explicit rc2 (cruft::view<u08 const*> key);
 
-        std::array<word_t,4> encrypt (std::array<word_t,4> src) const;
-        std::array<word_t,4> decrypt (std::array<word_t,4> src) const;
+        block_t encrypt (block_t src) const noexcept;
+        block_t decrypt (block_t src) const noexcept;
 
     private:
         std::array<u16,64> m_key;
diff --git a/test/block/rc2.cpp b/test/block/rc2.cpp
index f1c59fd..cecff1d 100644
--- a/test/block/rc2.cpp
+++ b/test/block/rc2.cpp
@@ -1,3 +1,123 @@
+#include <cruft/util/tap.hpp>
+
 #include "block/rc2.hpp"
 
-int main () { }
\ No newline at end of file
+#include <cruft/util/endian.hpp>
+
+
+int main ()
+{
+    struct {
+        unsigned effective;
+        std::vector<u08> key;
+        std::array<u16,4> plain;
+        std::array<u16,4> cipher;
+    } const TESTS[] = {
+        {
+            .effective = 63,
+            .key = { 0x00, 0x00, 0x00, 0x00,
+                     0x00, 0x00, 0x00, 0x00, },
+            .plain  = { 0x0000, 0x0000, 0x0000, 0x0000, },
+            .cipher = { 0xebb7, 0x73f9, 0x9327, 0x8eff, }
+        },
+
+        {
+            .effective = 64,
+            .key = { 0xff, 0xff, 0xff, 0xff,
+                     0xff, 0xff, 0xff, 0xff, },
+            .plain  = { 0xffff, 0xffff, 0xffff, 0xffff },
+            .cipher = { 0x278b, 0x27e4, 0x2e2f, 0x0d49 },
+        },
+
+        {
+            .effective = 64,
+            .key = { 0x30, 0x00, 0x00, 0x00,
+                     0x00, 0x00, 0x00, 0x00 },
+            .plain  = { 0x1000, 0x0000, 0x0000, 0x0001 },
+            .cipher = { 0x3064, 0x9edf, 0x9be7, 0xd2c2 },
+        },
+
+        {
+            .effective = 64,
+            .key    = { 0x88 },
+            .plain  = { 0x0000, 0x0000, 0x0000, 0x0000 },
+            .cipher = { 0x61a8, 0xa244, 0xadac, 0xccf0 },
+        },
+
+        {
+            .effective = 64,
+            .key = { 0x88, 0xbc, 0xa9, 0x0e,
+                     0x90, 0x87, 0x5a },
+            .plain  = { 0x0000, 0x0000, 0x0000, 0x0000, },
+            .cipher = { 0x6ccf, 0x4308, 0x974c, 0x267f, }
+        },
+
+        {
+            .effective = 64,
+            .key = { 0x88, 0xbc, 0xa9, 0x0e,
+                     0x90, 0x87, 0x5a, 0x7f,
+                     0x0f, 0x79, 0xc3, 0x84,
+                     0x62, 0x7b, 0xaf, 0xb2
+            },
+            .plain  = { 0x0000, 0x0000, 0x0000, 0x0000 },
+            .cipher = { 0x1a80, 0x7d27, 0x2bbe, 0x5db1 },
+        },
+
+        {
+            .effective = 128,
+            .key = {
+                0x88, 0xbc, 0xa9, 0x0e,
+                0x90, 0x87, 0x5a, 0x7f,
+                0x0f, 0x79, 0xc3, 0x84,
+                0x62, 0x7b, 0xaf, 0xb2,
+            },
+            .plain  = { 0x0000, 0x0000, 0x0000, 0x0000 },
+            .cipher = { 0x2269, 0x552a, 0xb0f8, 0x5ca6 },
+        },
+
+        {
+            .effective = 129,
+            .key = {
+                0x88, 0xbc, 0xa9, 0x0e,
+                0x90, 0x87, 0x5a, 0x7f,
+                0x0f, 0x79, 0xc3, 0x84,
+                0x62, 0x7b, 0xaf, 0xb2,
+                0x16, 0xf8, 0x0a, 0x6f,
+                0x85, 0x92, 0x05, 0x84,
+                0xc4, 0x2f, 0xce, 0xb0,
+                0xbe, 0x25, 0x5d, 0xaf,
+                0x1e
+            },
+            .plain  = { 0x0000, 0x0000, 0x0000, 0x0000 },
+            .cipher = { 0x5b78, 0xd3a4, 0x3dff, 0xf1f1 },
+        }
+    };
+
+
+    cruft::TAP::logger tap;
+
+    for (auto const &t: TESTS) {
+        cruft::crypto::block::rc2 const obj (t.key, t.effective);
+
+        std::array<u16,4> plain = t.plain;
+        std::transform (
+            std::begin (plain),
+            std::end   (plain),
+            std::begin (plain),
+            cruft::bswap<u16>
+        );
+
+        std::array<u16,4> cipher = t.cipher;
+        std::transform (
+            std::begin (cipher),
+            std::end   (cipher),
+            std::begin (cipher),
+            cruft::bswap<u16>
+        );
+
+        tap.expect (obj.encrypt (plain) == cipher, "rc2_enc");
+        tap.expect (obj.decrypt (cipher) == plain,  "rc2_dec");
+    }
+
+    return tap.status ();
+}