diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index fdce0fc..15d623f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,7 +17,7 @@ jobs:
       image: "erlang:${{matrix.otp_vsn}}"
     strategy:
       matrix:
-        otp_vsn: ["19.3", "21.3", "22.3", "23.2", "24.0"] # omitting 20.3 due to TLS issue
+        otp_vsn: ["19.3", "21.3", "22.3", "23.2", "24.0", "28"] # omitting 20.3 due to TLS issue
         os: ["ubuntu-latest"]
     steps:
       - uses: "actions/checkout@v2"
diff --git a/test/rfc4226_hotp_tests.erl b/test/rfc4226_hotp_tests.erl
new file mode 100644
index 0000000..43186e8
--- /dev/null
+++ b/test/rfc4226_hotp_tests.erl
@@ -0,0 +1,34 @@
+-module(rfc4226_hotp_tests).
+-author("Sebastien Merle").
+-include_lib("eunit/include/eunit.hrl").
+
+
+rfc4226_hotp_vectors_test_() ->
+    Secret = pot_base32:encode(rfc4226_secret()),
+    [{integer_to_list(Counter),
+      ?_assertEqual(Expected, pot:hotp(Secret, Counter))}
+     || {Counter, Expected} <- rfc4226_vectors()].
+
+
+% RFC4226 - Appendix D - HOTP Algorithm: Test Values
+% https://www.rfc-editor.org/rfc/rfc4226.html#page-32
+
+
+rfc4226_secret() ->
+    <<16#31, 16#32, 16#33, 16#34, 16#35,
+      16#36, 16#37, 16#38, 16#39, 16#30,
+      16#31, 16#32, 16#33, 16#34, 16#35,
+      16#36, 16#37, 16#38, 16#39, 16#30>>.
+
+
+rfc4226_vectors() ->
+    [{0, <<"755224">>},
+     {1, <<"287082">>},
+     {2, <<"359152">>},
+     {3, <<"969429">>},
+     {4, <<"338314">>},
+     {5, <<"254676">>},
+     {6, <<"287922">>},
+     {7, <<"162583">>},
+     {8, <<"399871">>},
+     {9, <<"520489">>}].
diff --git a/test/rfc6238_totp_tests.erl b/test/rfc6238_totp_tests.erl
new file mode 100644
index 0000000..ec2c280
--- /dev/null
+++ b/test/rfc6238_totp_tests.erl
@@ -0,0 +1,64 @@
+-module(rfc6238_totp_tests).
+-author("Sebastien Merle").
+-include_lib("eunit/include/eunit.hrl").
+
+
+rfc6238_totp_vectors_test_() ->
+    [{test_name(Algorithm, UnixSeconds),
+      ?_assertEqual(Expected, pot:totp(secret(Algorithm), opts(Algorithm, UnixSeconds)))}
+     || {UnixSeconds, Algorithm, Expected} <- rfc6238_vectors()].
+
+
+opts(Algorithm, UnixSeconds) ->
+    [{digest_method, Algorithm},
+     {token_length, 8},
+     {timestamp, timestamp(UnixSeconds)}].
+
+
+timestamp(UnixSeconds) ->
+    {UnixSeconds div 1000000, UnixSeconds rem 1000000, 0}.
+
+
+test_name(Algorithm, UnixSeconds) ->
+    atom_to_list(Algorithm) ++ " at " ++ integer_to_list(UnixSeconds).
+
+
+secret(sha) ->
+    pot_base32:encode(seed(sha));
+secret(sha256) ->
+    pot_base32:encode(seed(sha256));
+secret(sha512) ->
+    pot_base32:encode(seed(sha512)).
+
+
+% RFC6238 - Appendix B - Test Vectors
+% https://www.rfc-editor.org/rfc/rfc6238.html#appendix-B
+
+
+seed(sha) ->
+    <<"12345678901234567890">>;
+seed(sha256) ->
+    <<"12345678901234567890123456789012">>;
+seed(sha512) ->
+    <<"1234567890123456789012345678901234567890123456789012345678901234">>.
+
+
+rfc6238_vectors() ->
+    [{59, sha, <<"94287082">>},
+     {59, sha256, <<"46119246">>},
+     {59, sha512, <<"90693936">>},
+     {1111111109, sha, <<"07081804">>},
+     {1111111109, sha256, <<"68084774">>},
+     {1111111109, sha512, <<"25091201">>},
+     {1111111111, sha, <<"14050471">>},
+     {1111111111, sha256, <<"67062674">>},
+     {1111111111, sha512, <<"99943326">>},
+     {1234567890, sha, <<"89005924">>},
+     {1234567890, sha256, <<"91819424">>},
+     {1234567890, sha512, <<"93441116">>},
+     {2000000000, sha, <<"69279037">>},
+     {2000000000, sha256, <<"90698825">>},
+     {2000000000, sha512, <<"38618901">>},
+     {20000000000, sha, <<"65353130">>},
+     {20000000000, sha256, <<"77737706">>},
+     {20000000000, sha512, <<"47863826">>}].