diff --git a/Data/Digest/Pure/SHA.hs b/Data/Digest/Pure/SHA.hs
--- a/Data/Digest/Pure/SHA.hs
+++ b/Data/Digest/Pure/SHA.hs
@@ -3,15 +3,23 @@
 -- is basically an unoptimized translation of FIPS 180-2 into Haskell. If you're
 -- looking for performance, you probably won't find it here.
 module Data.Digest.Pure.SHA
-       ( Digest
+       ( -- * 'Digest' and related functions
+         Digest
+       , showDigest
+       , integerDigest
+       , bytestringDigest
+         -- * Calculating hashes
        , sha1
        , sha224
        , sha256
        , sha384
        , sha512
-       , showDigest
-       , integerDigest
-       , bytestringDigest
+         -- * Calculating message authentication codes (MACs)
+       , hmacSha1
+       , hmacSha224
+       , hmacSha256
+       , hmacSha384
+       , hmacSha512
 #ifdef SHA_TEST
        , toBigEndianBS, fromBigEndianBS
        , calc_k
@@ -919,6 +927,61 @@
   bs_pad = padSHA512 bs_in
   fstate = runSHA initialSHA512State processSHA512Block bs_pad
   bs_out = runPut $ synthesizeSHA512 fstate
+
+-- --------------------------------------------------------------------------
+
+-- | Compute an HMAC using SHA-1.
+hmacSha1
+  :: ByteString  -- ^ secret key
+  -> ByteString  -- ^ message
+  -> Digest      -- ^ SHA-1 MAC
+hmacSha1 = hmac sha1 64
+
+-- | Compute an HMAC using SHA-224.
+hmacSha224
+  :: ByteString  -- ^ secret key
+  -> ByteString  -- ^ message
+  -> Digest      -- ^ SHA-224 MAC
+hmacSha224 = hmac sha224 64
+
+-- | Compute an HMAC using SHA-256.
+hmacSha256
+  :: ByteString  -- ^ secret key
+  -> ByteString  -- ^ message
+  -> Digest      -- ^ SHA-256 MAC
+hmacSha256 = hmac sha256 64
+
+-- | Compute an HMAC using SHA-384.
+hmacSha384
+  :: ByteString  -- ^ secret key
+  -> ByteString  -- ^ message
+  -> Digest      -- ^ SHA-384 MAC
+hmacSha384 = hmac sha384 128
+
+-- | Compute an HMAC using SHA-512.
+hmacSha512
+  :: ByteString  -- ^ secret key
+  -> ByteString  -- ^ message
+  -> Digest      -- ^ SHA-512 MAC
+hmacSha512 = hmac sha512 128
+
+-- --------------------------------------------------------------------------
+
+hmac :: (ByteString -> Digest) -> Int -> ByteString -> ByteString -> Digest
+hmac f bl k m = f (BS.append opad (bytestringDigest (f (BS.append ipad m))))
+ where
+  opad = BS.map (xor ov) k'
+  ipad = BS.map (xor iv) k'
+  ov = 0x5c :: Word8
+  iv = 0x36 :: Word8
+
+  k' = BS.append kt pad
+   where
+    kt  = if kn > bn then bytestringDigest (f k) else k
+    pad = BS.replicate (bn - ktn) 0
+    kn  = fromIntegral (BS.length k)
+    ktn = fromIntegral (BS.length kt)
+    bn  = fromIntegral bl
 
 -- --------------------------------------------------------------------------
 --
diff --git a/SHA.cabal b/SHA.cabal
--- a/SHA.cabal
+++ b/SHA.cabal
@@ -1,9 +1,9 @@
 name:       SHA
 category:   Cryptography, Codec
-version:    1.2.1
+version:    1.4.0
 license:    BSD3
 license-file: LICENSE
-author:     Adam Wick <awick@galois.com>
+author:     Adam Wick <awick@galois.com>, Brian Lewis <brian@lorf.org>
 maintainer: Adam Wick <awick@galois.com>
 stability:  stable
 build-type: Simple
@@ -11,11 +11,12 @@
 tested-with: GHC ==6.8.0
 synopsis: Implementations of the SHA suite of message digest functions
 description: This library implements the SHA suite of message digest functions,
-             according to NIST FIPS 180-2 (with the SHA-224 addendum). The
-             functions have been tested against most of the NIST test vectors
-             for the various functions. While some attention has been paid to
-             performance, these do not presently reach the speed of
-             well-tuned libraries, like OpenSSL.
+             according to NIST FIPS 180-2 (with the SHA-224 addendum), as well
+             as the SHA-based HMAC routines. The functions have been tested 
+             against most of the NIST and RFC test vectors for the various
+             functions. While some attention has been paid to performance, 
+             these do not presently reach the speed of well-tuned libraries, 
+             like OpenSSL.
 
 Flag Test
  Description: Build the SHA test suite.
diff --git a/Test.hs b/Test.hs
# file too large to diff: Test.hs