diff --git a/doc/crypto.dox b/doc/crypto.dox
index 63158c47..b793611d 100644
--- a/doc/crypto.dox
+++ b/doc/crypto.dox
@@ -29,7 +29,7 @@
 \li Block ciphers: AES128, AES192, AES256
 \li Block cipher modes: CTR, CFB, CBC, OFB
 \li Stream ciphers: ChaCha
-\li Hash algorithms: SHA1, SHA256, SHA512, SHA3_256, SHA3_512, BLAKE2s, BLAKE2b
+\li Hash algorithms: SHA1, SHA256, SHA512, SHA3_256, SHA3_512, BLAKE2s, BLAKE2b (regular and HMAC modes)
 \li Public key algorithms: Curve25519
 \li Random number generation: \link RNGClass RNG\endlink, TransistorNoiseSource, RingOscillatorNoiseSource
 
diff --git a/doc/mainpage.dox b/doc/mainpage.dox
index 87cbf1d7..57f6554e 100644
--- a/doc/mainpage.dox
+++ b/doc/mainpage.dox
@@ -93,7 +93,7 @@ realtime clock and the LCD library to implement an alarm clock.
 \li Block ciphers: AES128, AES192, AES256
 \li Block cipher modes: CTR, CFB, CBC, OFB
 \li Stream ciphers: ChaCha
-\li Hash algorithms: SHA1, SHA256, SHA512, SHA3_256, SHA3_512, BLAKE2s, BLAKE2b
+\li Hash algorithms: SHA1, SHA256, SHA512, SHA3_256, SHA3_512, BLAKE2s, BLAKE2b (regular and HMAC modes)
 \li Public key algorithms: Curve25519
 \li Random number generation: \link RNGClass RNG\endlink, TransistorNoiseSource, RingOscillatorNoiseSource
 
diff --git a/libraries/Crypto/BLAKE2b.cpp b/libraries/Crypto/BLAKE2b.cpp
index 569cb518..3c21e3c1 100644
--- a/libraries/Crypto/BLAKE2b.cpp
+++ b/libraries/Crypto/BLAKE2b.cpp
@@ -162,6 +162,25 @@ void BLAKE2b::clear()
     reset();
 }
 
+void BLAKE2b::resetHMAC(const void *key, size_t keyLen)
+{
+    formatHMACKey(state.m, key, keyLen, 0x36);
+    state.lengthLow += 128;
+    processChunk(0);
+}
+
+void BLAKE2b::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
+{
+    uint8_t temp[64];
+    finalize(temp, sizeof(temp));
+    formatHMACKey(state.m, key, keyLen, 0x5C);
+    state.lengthLow += 128;
+    processChunk(0);
+    update(temp, sizeof(temp));
+    finalize(hash, hashLen);
+    clean(temp);
+}
+
 // Permutation on the message input state for BLAKE2b.
 static const uint8_t sigma[12][16] PROGMEM = {
     { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15},
diff --git a/libraries/Crypto/BLAKE2b.h b/libraries/Crypto/BLAKE2b.h
index 67d7e887..db9964a8 100644
--- a/libraries/Crypto/BLAKE2b.h
+++ b/libraries/Crypto/BLAKE2b.h
@@ -41,6 +41,9 @@ class BLAKE2b : public Hash
 
     void clear();
 
+    void resetHMAC(const void *key, size_t keyLen);
+    void finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen);
+
 private:
     struct {
         uint64_t h[8];
diff --git a/libraries/Crypto/BLAKE2s.cpp b/libraries/Crypto/BLAKE2s.cpp
index a3244611..26bdd548 100644
--- a/libraries/Crypto/BLAKE2s.cpp
+++ b/libraries/Crypto/BLAKE2s.cpp
@@ -157,6 +157,25 @@ void BLAKE2s::clear()
     reset();
 }
 
+void BLAKE2s::resetHMAC(const void *key, size_t keyLen)
+{
+    formatHMACKey(state.m, key, keyLen, 0x36);
+    state.length += 64;
+    processChunk(0);
+}
+
+void BLAKE2s::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
+{
+    uint8_t temp[32];
+    finalize(temp, sizeof(temp));
+    formatHMACKey(state.m, key, keyLen, 0x5C);
+    state.length += 64;
+    processChunk(0);
+    update(temp, sizeof(temp));
+    finalize(hash, hashLen);
+    clean(temp);
+}
+
 // Permutation on the message input state for BLAKE2s.
 static const uint8_t sigma[10][16] PROGMEM = {
     { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15},
diff --git a/libraries/Crypto/BLAKE2s.h b/libraries/Crypto/BLAKE2s.h
index a996fff1..baece681 100644
--- a/libraries/Crypto/BLAKE2s.h
+++ b/libraries/Crypto/BLAKE2s.h
@@ -41,6 +41,9 @@ class BLAKE2s : public Hash
 
     void clear();
 
+    void resetHMAC(const void *key, size_t keyLen);
+    void finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen);
+
 private:
     struct {
         uint32_t h[8];
diff --git a/libraries/Crypto/Hash.cpp b/libraries/Crypto/Hash.cpp
index f0f3b3ab..57432a8e 100644
--- a/libraries/Crypto/Hash.cpp
+++ b/libraries/Crypto/Hash.cpp
@@ -21,6 +21,7 @@
  */
 
 #include "Hash.h"
+#include <string.h>
 
 /**
  * \class Hash Hash.h <Hash.h>
@@ -66,7 +67,7 @@ Hash::~Hash()
  * \fn void Hash::reset()
  * \brief Resets the hash ready for a new hashing process.
  *
- * \sa update(), finalize()
+ * \sa update(), finalize(), resetHMAC()
  */
 
 /**
@@ -96,7 +97,7 @@ Hash::~Hash()
  * If finalize() is called again, then the returned \a hash value is
  * undefined.  Call reset() first to start a new hashing process.
  *
- * \sa reset(), update()
+ * \sa reset(), update(), finalizeHMAC()
  */
 
 /**
@@ -106,3 +107,74 @@ Hash::~Hash()
  *
  * \sa reset()
  */
+
+/**
+ * \fn void Hash::resetHMAC(const void *key, size_t keyLen)
+ * \brief Resets the hash ready for a new HMAC hashing process.
+ *
+ * \param key Points to the HMAC key for the hashing process.
+ * \param keyLen Size of the HMAC \a key in bytes.
+ *
+ * The following example computes a HMAC over a series of data blocks
+ * with a specific key:
+ *
+ * \code
+ * hash.resetHMAC(key, sizeof(key));
+ * hash.update(data1, sizeof(data1));
+ * hash.update(data2, sizeof(data2));
+ * ...
+ * hash.update(dataN, sizeof(dataN));
+ * hash.finalizeHMAC(key, sizeof(key), hmac, sizeof(hmac));
+ * \endcode
+ *
+ * The same key must be passed to both resetHMAC() and finalizeHMAC().
+ *
+ * \sa finalizeHMAC(), reset()
+ */
+
+/**
+ * \fn void Hash::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
+ * \brief Finalizes the HMAC hashing process and returns the hash.
+ *
+ * \param key Points to the HMAC key for the hashing process.  The contents
+ * of this array must be identical to the value passed to resetHMAC().
+ * \param keyLen Size of the HMAC \a key in bytes.
+ * \param hash The buffer to return the hash value in.
+ * \param hashLen The length of the \a hash buffer, normally hashSize().
+ *
+ * \sa resetHMAC(), finalize()
+ */
+
+/**
+ * \brief Formats a HMAC key into a block.
+ *
+ * \param block The block to format the key into.  Must be at least
+ * blockSize() bytes in length.
+ * \param key Points to the HMAC key for the hashing process.
+ * \param len Length of the HMAC \a key in bytes.
+ * \param pad Inner (0x36) or outer (0x5C) padding value to XOR with
+ * the formatted HMAC key.
+ *
+ * This function is intended to help subclasses implement resetHMAC() and
+ * finalizeHMAC() by directly formatting the HMAC key into the subclass's
+ * internal block buffer and resetting the hash.
+ */
+void Hash::formatHMACKey(void *block, const void *key, size_t len, uint8_t pad)
+{
+    size_t size = blockSize();
+    reset();
+    if (len <= size) {
+        memcpy(block, key, len);
+    } else {
+        update(key, len);
+        len = hashSize();
+        finalize(block, len);
+        reset();
+    }
+    memset(block + len, pad, size - len);
+    uint8_t *b = (uint8_t *)block;
+    while (len > 0) {
+        *b++ ^= pad;
+        --len;
+    }
+}
diff --git a/libraries/Crypto/Hash.h b/libraries/Crypto/Hash.h
index 2d42f41c..2f7db16a 100644
--- a/libraries/Crypto/Hash.h
+++ b/libraries/Crypto/Hash.h
@@ -40,6 +40,12 @@ class Hash
     virtual void finalize(void *hash, size_t len) = 0;
 
     virtual void clear() = 0;
+
+    virtual void resetHMAC(const void *key, size_t keyLen) = 0;
+    virtual void finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen) = 0;
+
+protected:
+    void formatHMACKey(void *block, const void *key, size_t len, uint8_t pad);
 };
 
 #endif
diff --git a/libraries/Crypto/KeccakCore.cpp b/libraries/Crypto/KeccakCore.cpp
index 9c18f870..eeaa56ad 100644
--- a/libraries/Crypto/KeccakCore.cpp
+++ b/libraries/Crypto/KeccakCore.cpp
@@ -247,6 +247,41 @@ void KeccakCore::clear()
     clean(state);
 }
 
+/**
+ * \brief Sets a HMAC key for a Keccak-based hash algorithm.
+ *
+ * \param key Points to the HMAC key for the hashing process.
+ * \param len Length of the HMAC \a key in bytes.
+ * \param pad Inner (0x36) or outer (0x5C) padding value to XOR with
+ * the formatted HMAC key.
+ * \param hashSize The size of the output from the hash algorithm.
+ *
+ * This function is intended to help classes implement Hash::resetHMAC() and
+ * Hash::finalizeHMAC() by directly formatting the HMAC key into the
+ * internal block buffer and resetting the hash.
+ */
+void KeccakCore::setHMACKey(const void *key, size_t len, uint8_t pad, size_t hashSize)
+{
+    uint8_t *b = (uint8_t *)state.B;
+    size_t size = blockSize();
+    reset();
+    if (len <= size) {
+        memcpy(b, key, len);
+    } else {
+        update(key, len);
+        this->pad(0x06);
+        extract(b, hashSize);
+        len = hashSize;
+        reset();
+    }
+    memset(b + len, pad, size - len);
+    while (len > 0) {
+        *b++ ^= pad;
+        --len;
+    }
+    update(state.B, size);
+}
+
 /**
  * \brief Transform the state with the KECCAK-p sponge function with b = 1600.
  */
diff --git a/libraries/Crypto/KeccakCore.h b/libraries/Crypto/KeccakCore.h
index 607447d1..d2a0464c 100644
--- a/libraries/Crypto/KeccakCore.h
+++ b/libraries/Crypto/KeccakCore.h
@@ -46,6 +46,8 @@ class KeccakCore
 
     void clear();
 
+    void setHMACKey(const void *key, size_t len, uint8_t pad, size_t hashSize);
+
 private:
     struct {
         uint64_t A[5][5];
diff --git a/libraries/Crypto/SHA1.cpp b/libraries/Crypto/SHA1.cpp
index ab5ac575..9d212068 100644
--- a/libraries/Crypto/SHA1.cpp
+++ b/libraries/Crypto/SHA1.cpp
@@ -131,6 +131,25 @@ void SHA1::clear()
     reset();
 }
 
+void SHA1::resetHMAC(const void *key, size_t keyLen)
+{
+    formatHMACKey(state.w, key, keyLen, 0x36);
+    state.length += 64 * 8;
+    processChunk();
+}
+
+void SHA1::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
+{
+    uint8_t temp[20];
+    finalize(temp, sizeof(temp));
+    formatHMACKey(state.w, key, keyLen, 0x5C);
+    state.length += 64 * 8;
+    processChunk();
+    update(temp, sizeof(temp));
+    finalize(hash, hashLen);
+    clean(temp);
+}
+
 /**
  * \brief Processes a single 512-bit chunk with the core SHA-1 algorithm.
  *
diff --git a/libraries/Crypto/SHA1.h b/libraries/Crypto/SHA1.h
index 1a81a0cb..328ca39a 100644
--- a/libraries/Crypto/SHA1.h
+++ b/libraries/Crypto/SHA1.h
@@ -40,6 +40,9 @@ class SHA1 : public Hash
 
     void clear();
 
+    void resetHMAC(const void *key, size_t keyLen);
+    void finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen);
+
 private:
     struct {
         uint32_t h[5];
diff --git a/libraries/Crypto/SHA256.cpp b/libraries/Crypto/SHA256.cpp
index 26b1b500..1c877936 100644
--- a/libraries/Crypto/SHA256.cpp
+++ b/libraries/Crypto/SHA256.cpp
@@ -136,6 +136,25 @@ void SHA256::clear()
     reset();
 }
 
+void SHA256::resetHMAC(const void *key, size_t keyLen)
+{
+    formatHMACKey(state.w, key, keyLen, 0x36);
+    state.length += 64 * 8;
+    processChunk();
+}
+
+void SHA256::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
+{
+    uint8_t temp[32];
+    finalize(temp, sizeof(temp));
+    formatHMACKey(state.w, key, keyLen, 0x5C);
+    state.length += 64 * 8;
+    processChunk();
+    update(temp, sizeof(temp));
+    finalize(hash, hashLen);
+    clean(temp);
+}
+
 /**
  * \brief Processes a single 512-bit chunk with the core SHA-256 algorithm.
  *
diff --git a/libraries/Crypto/SHA256.h b/libraries/Crypto/SHA256.h
index c4a2504b..246ea586 100644
--- a/libraries/Crypto/SHA256.h
+++ b/libraries/Crypto/SHA256.h
@@ -40,6 +40,9 @@ class SHA256 : public Hash
 
     void clear();
 
+    void resetHMAC(const void *key, size_t keyLen);
+    void finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen);
+
 private:
     struct {
         uint32_t h[8];
diff --git a/libraries/Crypto/SHA3.cpp b/libraries/Crypto/SHA3.cpp
index 684d267f..74353c44 100644
--- a/libraries/Crypto/SHA3.cpp
+++ b/libraries/Crypto/SHA3.cpp
@@ -21,6 +21,7 @@
  */
 
 #include "SHA3.h"
+#include "Crypto.h"
 
 /**
  * \class SHA3_256 SHA3.h <SHA3.h>
@@ -79,6 +80,21 @@ void SHA3_256::clear()
     core.clear();
 }
 
+void SHA3_256::resetHMAC(const void *key, size_t keyLen)
+{
+    core.setHMACKey(key, keyLen, 0x36, 32);
+}
+
+void SHA3_256::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
+{
+    uint8_t temp[32];
+    finalize(temp, sizeof(temp));
+    core.setHMACKey(key, keyLen, 0x5C, 32);
+    core.update(temp, sizeof(temp));
+    finalize(hash, hashLen);
+    clean(temp);
+}
+
 /**
  * \class SHA3_512 SHA3.h <SHA3.h>
  * \brief SHA3-512 hash algorithm.
@@ -135,3 +151,18 @@ void SHA3_512::clear()
 {
     core.clear();
 }
+
+void SHA3_512::resetHMAC(const void *key, size_t keyLen)
+{
+    core.setHMACKey(key, keyLen, 0x36, 64);
+}
+
+void SHA3_512::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
+{
+    uint8_t temp[64];
+    finalize(temp, sizeof(temp));
+    core.setHMACKey(key, keyLen, 0x5C, 64);
+    core.update(temp, sizeof(temp));
+    finalize(hash, hashLen);
+    clean(temp);
+}
diff --git a/libraries/Crypto/SHA3.h b/libraries/Crypto/SHA3.h
index bb19643f..76bb031c 100644
--- a/libraries/Crypto/SHA3.h
+++ b/libraries/Crypto/SHA3.h
@@ -41,6 +41,9 @@ class SHA3_256 : public Hash
 
     void clear();
 
+    void resetHMAC(const void *key, size_t keyLen);
+    void finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen);
+
 private:
     KeccakCore core;
 };
@@ -60,6 +63,9 @@ class SHA3_512 : public Hash
 
     void clear();
 
+    void resetHMAC(const void *key, size_t keyLen);
+    void finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen);
+
 private:
     KeccakCore core;
 };
diff --git a/libraries/Crypto/SHA512.cpp b/libraries/Crypto/SHA512.cpp
index cfe8859c..1176ef96 100644
--- a/libraries/Crypto/SHA512.cpp
+++ b/libraries/Crypto/SHA512.cpp
@@ -139,6 +139,25 @@ void SHA512::clear()
     reset();
 }
 
+void SHA512::resetHMAC(const void *key, size_t keyLen)
+{
+    formatHMACKey(state.w, key, keyLen, 0x36);
+    state.lengthLow += 128 * 8;
+    processChunk();
+}
+
+void SHA512::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
+{
+    uint8_t temp[64];
+    finalize(temp, sizeof(temp));
+    formatHMACKey(state.w, key, keyLen, 0x5C);
+    state.lengthLow += 128 * 8;
+    processChunk();
+    update(temp, sizeof(temp));
+    finalize(hash, hashLen);
+    clean(temp);
+}
+
 /**
  * \brief Processes a single 1024-bit chunk with the core SHA-512 algorithm.
  *
diff --git a/libraries/Crypto/SHA512.h b/libraries/Crypto/SHA512.h
index d394ae45..1530d548 100644
--- a/libraries/Crypto/SHA512.h
+++ b/libraries/Crypto/SHA512.h
@@ -40,6 +40,9 @@ class SHA512 : public Hash
 
     void clear();
 
+    void resetHMAC(const void *key, size_t keyLen);
+    void finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen);
+
 private:
     struct {
         uint64_t h[8];
diff --git a/libraries/Crypto/examples/TestBLAKE2b/TestBLAKE2b.ino b/libraries/Crypto/examples/TestBLAKE2b/TestBLAKE2b.ino
index e40c0a92..fa2a1bbc 100644
--- a/libraries/Crypto/examples/TestBLAKE2b/TestBLAKE2b.ino
+++ b/libraries/Crypto/examples/TestBLAKE2b/TestBLAKE2b.ino
@@ -29,6 +29,7 @@ This example runs tests on the BLAKE2b implementation to verify correct behaviou
 #include <string.h>
 
 #define HASH_SIZE 64
+#define BLOCK_SIZE 128
 
 struct TestHashVector
 {
@@ -90,7 +91,7 @@ static TestHashVector const testVectorBLAKE2b_4 = {
 
 BLAKE2b blake2b;
 
-byte buffer[128];
+byte buffer[BLOCK_SIZE + 2];
 
 bool testHash_N(Hash *hash, const struct TestHashVector *test, size_t inc)
 {
@@ -160,6 +161,69 @@ void perfHash(Hash *hash)
     Serial.println(" bytes per second");
 }
 
+// Very simple method for hashing a HMAC inner or outer key.
+void hashKey(Hash *hash, const uint8_t *key, size_t keyLen, uint8_t pad)
+{
+    size_t posn;
+    uint8_t buf;
+    uint8_t result[HASH_SIZE];
+    if (keyLen <= BLOCK_SIZE) {
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < keyLen)
+                buf = key[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    } else {
+        hash->reset();
+        hash->update(key, keyLen);
+        hash->finalize(result, HASH_SIZE);
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < HASH_SIZE)
+                buf = result[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    }
+}
+
+void testHMAC(Hash *hash, size_t keyLen)
+{
+    uint8_t result[HASH_SIZE];
+
+    Serial.print("HMAC-BLAKE2b keysize=");
+    Serial.print(keyLen);
+    Serial.print(" ... ");
+
+    // Construct the expected result with a simple HMAC implementation.
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x36);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    hash->finalize(result, HASH_SIZE);
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x5C);
+    hash->update(result, HASH_SIZE);
+    hash->finalize(result, HASH_SIZE);
+
+    // Now use the library to compute the HMAC.
+    hash->resetHMAC(buffer, keyLen);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hash->finalizeHMAC(buffer, keyLen, buffer, HASH_SIZE);
+
+    // Check the result.
+    if (!memcmp(result, buffer, HASH_SIZE))
+        Serial.println("Passed");
+    else
+        Serial.println("Failed");
+}
+
 void setup()
 {
     Serial.begin(9600);
@@ -171,6 +235,12 @@ void setup()
     testHash(&blake2b, &testVectorBLAKE2b_2);
     testHash(&blake2b, &testVectorBLAKE2b_3);
     testHash(&blake2b, &testVectorBLAKE2b_4);
+    testHMAC(&blake2b, (size_t)0);
+    testHMAC(&blake2b, 1);
+    testHMAC(&blake2b, HASH_SIZE);
+    testHMAC(&blake2b, BLOCK_SIZE);
+    testHMAC(&blake2b, BLOCK_SIZE + 1);
+    testHMAC(&blake2b, BLOCK_SIZE + 2);
 
     Serial.println();
 
diff --git a/libraries/Crypto/examples/TestBLAKE2s/TestBLAKE2s.ino b/libraries/Crypto/examples/TestBLAKE2s/TestBLAKE2s.ino
index 26d4c9ee..9b7098e9 100644
--- a/libraries/Crypto/examples/TestBLAKE2s/TestBLAKE2s.ino
+++ b/libraries/Crypto/examples/TestBLAKE2s/TestBLAKE2s.ino
@@ -29,6 +29,7 @@ This example runs tests on the BLAKE2s implementation to verify correct behaviou
 #include <string.h>
 
 #define HASH_SIZE 32
+#define BLOCK_SIZE 64
 
 struct TestHashVector
 {
@@ -144,6 +145,69 @@ void perfHash(Hash *hash)
     Serial.println(" bytes per second");
 }
 
+// Very simple method for hashing a HMAC inner or outer key.
+void hashKey(Hash *hash, const uint8_t *key, size_t keyLen, uint8_t pad)
+{
+    size_t posn;
+    uint8_t buf;
+    uint8_t result[HASH_SIZE];
+    if (keyLen <= BLOCK_SIZE) {
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < keyLen)
+                buf = key[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    } else {
+        hash->reset();
+        hash->update(key, keyLen);
+        hash->finalize(result, HASH_SIZE);
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < HASH_SIZE)
+                buf = result[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    }
+}
+
+void testHMAC(Hash *hash, size_t keyLen)
+{
+    uint8_t result[HASH_SIZE];
+
+    Serial.print("HMAC-BLAKE2s keysize=");
+    Serial.print(keyLen);
+    Serial.print(" ... ");
+
+    // Construct the expected result with a simple HMAC implementation.
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x36);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    hash->finalize(result, HASH_SIZE);
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x5C);
+    hash->update(result, HASH_SIZE);
+    hash->finalize(result, HASH_SIZE);
+
+    // Now use the library to compute the HMAC.
+    hash->resetHMAC(buffer, keyLen);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hash->finalizeHMAC(buffer, keyLen, buffer, HASH_SIZE);
+
+    // Check the result.
+    if (!memcmp(result, buffer, HASH_SIZE))
+        Serial.println("Passed");
+    else
+        Serial.println("Failed");
+}
+
 void setup()
 {
     Serial.begin(9600);
@@ -155,6 +219,12 @@ void setup()
     testHash(&blake2s, &testVectorBLAKE2s_2);
     testHash(&blake2s, &testVectorBLAKE2s_3);
     testHash(&blake2s, &testVectorBLAKE2s_4);
+    testHMAC(&blake2s, (size_t)0);
+    testHMAC(&blake2s, 1);
+    testHMAC(&blake2s, HASH_SIZE);
+    testHMAC(&blake2s, BLOCK_SIZE);
+    testHMAC(&blake2s, BLOCK_SIZE + 1);
+    testHMAC(&blake2s, sizeof(buffer));
 
     Serial.println();
 
diff --git a/libraries/Crypto/examples/TestSHA1/TestSHA1.ino b/libraries/Crypto/examples/TestSHA1/TestSHA1.ino
index da398f1a..36c0670d 100644
--- a/libraries/Crypto/examples/TestSHA1/TestSHA1.ino
+++ b/libraries/Crypto/examples/TestSHA1/TestSHA1.ino
@@ -29,16 +29,19 @@ This example runs tests on the SHA1 implementation to verify correct behaviour.
 #include <string.h>
 
 #define HASH_SIZE 20
+#define BLOCK_SIZE 64
 
 struct TestHashVector
 {
     const char *name;
+    const char *key;
     const char *data;
     uint8_t hash[HASH_SIZE];
 };
 
 static TestHashVector const testVectorSHA1_1 = {
     "SHA-1 #1",
+    0,
     "abc",
     {0xA9, 0x99, 0x3E, 0x36, 0x47, 0x06, 0x81, 0x6A,
      0xBA, 0x3E, 0x25, 0x71, 0x78, 0x50, 0xC2, 0x6C,
@@ -46,11 +49,28 @@ static TestHashVector const testVectorSHA1_1 = {
 };
 static TestHashVector const testVectorSHA1_2 = {
     "SHA-1 #2",
+    0,
     "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq",
     {0x84, 0x98, 0x3E, 0x44, 0x1C, 0x3B, 0xD2, 0x6E,
      0xBA, 0xAE, 0x4A, 0xA1, 0xF9, 0x51, 0x29, 0xE5,
      0xE5, 0x46, 0x70, 0xF1}
 };
+static TestHashVector const testVectorHMAC_SHA1_1 = {
+    "HMAC-SHA-1 #1",
+    "",
+    "",
+    {0xfb, 0xdb, 0x1d, 0x1b, 0x18, 0xaa, 0x6c, 0x08,
+     0x32, 0x4b, 0x7d, 0x64, 0xb7, 0x1f, 0xb7, 0x63,
+     0x70, 0x69, 0x0e, 0x1d}
+};
+static TestHashVector const testVectorHMAC_SHA1_2 = {
+    "HMAC-SHA-1 #2",
+    "key",
+    "The quick brown fox jumps over the lazy dog",
+    {0xde, 0x7c, 0x9b, 0x85, 0xb8, 0xb7, 0x8a, 0xa6,
+     0xbc, 0x8a, 0x7a, 0x36, 0xf7, 0x0a, 0x90, 0x70,
+     0x1c, 0x9d, 0xb4, 0xd9}
+};
 
 SHA1 sha1;
 
@@ -100,6 +120,86 @@ void testHash(Hash *hash, const struct TestHashVector *test)
         Serial.println("Failed");
 }
 
+// Very simple method for hashing a HMAC inner or outer key.
+void hashKey(Hash *hash, const uint8_t *key, size_t keyLen, uint8_t pad)
+{
+    size_t posn;
+    uint8_t buf;
+    uint8_t result[HASH_SIZE];
+    if (keyLen <= BLOCK_SIZE) {
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < keyLen)
+                buf = key[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    } else {
+        hash->reset();
+        hash->update(key, keyLen);
+        hash->finalize(result, HASH_SIZE);
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < HASH_SIZE)
+                buf = result[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    }
+}
+
+void testHMAC(Hash *hash, size_t keyLen)
+{
+    uint8_t result[HASH_SIZE];
+
+    Serial.print("HMAC-SHA-1 keysize=");
+    Serial.print(keyLen);
+    Serial.print(" ... ");
+
+    // Construct the expected result with a simple HMAC implementation.
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x36);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    hash->finalize(result, HASH_SIZE);
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x5C);
+    hash->update(result, HASH_SIZE);
+    hash->finalize(result, HASH_SIZE);
+
+    // Now use the library to compute the HMAC.
+    hash->resetHMAC(buffer, keyLen);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hash->finalizeHMAC(buffer, keyLen, buffer, HASH_SIZE);
+
+    // Check the result.
+    if (!memcmp(result, buffer, HASH_SIZE))
+        Serial.println("Passed");
+    else
+        Serial.println("Failed");
+}
+
+void testHMAC(Hash *hash, const struct TestHashVector *test)
+{
+    uint8_t result[HASH_SIZE];
+
+    Serial.print(test->name);
+    Serial.print(" ... ");
+
+    hash->resetHMAC(test->key, strlen(test->key));
+    hash->update(test->data, strlen(test->data));
+    hash->finalizeHMAC(test->key, strlen(test->key), result, sizeof(result));
+
+    if (!memcmp(result, test->hash, HASH_SIZE))
+        Serial.println("Passed");
+    else
+        Serial.println("Failed");
+}
+
 void perfHash(Hash *hash)
 {
     unsigned long start;
@@ -133,6 +233,14 @@ void setup()
     Serial.println("Test Vectors:");
     testHash(&sha1, &testVectorSHA1_1);
     testHash(&sha1, &testVectorSHA1_2);
+    testHMAC(&sha1, &testVectorHMAC_SHA1_1);
+    testHMAC(&sha1, &testVectorHMAC_SHA1_2);
+    testHMAC(&sha1, (size_t)0);
+    testHMAC(&sha1, 1);
+    testHMAC(&sha1, HASH_SIZE);
+    testHMAC(&sha1, BLOCK_SIZE);
+    testHMAC(&sha1, BLOCK_SIZE + 1);
+    testHMAC(&sha1, sizeof(buffer));
 
     Serial.println();
 
diff --git a/libraries/Crypto/examples/TestSHA256/TestSHA256.ino b/libraries/Crypto/examples/TestSHA256/TestSHA256.ino
index 6117ee2b..4bec5add 100644
--- a/libraries/Crypto/examples/TestSHA256/TestSHA256.ino
+++ b/libraries/Crypto/examples/TestSHA256/TestSHA256.ino
@@ -29,16 +29,19 @@ This example runs tests on the SHA256 implementation to verify correct behaviour
 #include <string.h>
 
 #define HASH_SIZE 32
+#define BLOCK_SIZE 64
 
 struct TestHashVector
 {
     const char *name;
+    const char *key;
     const char *data;
     uint8_t hash[HASH_SIZE];
 };
 
 static TestHashVector const testVectorSHA256_1 = {
     "SHA-256 #1",
+    0,
     "abc",
     {0xba, 0x78, 0x16, 0xbf, 0x8f, 0x01, 0xcf, 0xea,
      0x41, 0x41, 0x40, 0xde, 0x5d, 0xae, 0x22, 0x23,
@@ -47,12 +50,31 @@ static TestHashVector const testVectorSHA256_1 = {
 };
 static TestHashVector const testVectorSHA256_2 = {
     "SHA-256 #2",
+    0,
     "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq",
     {0x24, 0x8d, 0x6a, 0x61, 0xd2, 0x06, 0x38, 0xb8,
      0xe5, 0xc0, 0x26, 0x93, 0x0c, 0x3e, 0x60, 0x39,
      0xa3, 0x3c, 0xe4, 0x59, 0x64, 0xff, 0x21, 0x67,
      0xf6, 0xec, 0xed, 0xd4, 0x19, 0xdb, 0x06, 0xc1}
 };
+static TestHashVector const testVectorHMAC_SHA256_1 = {
+    "HMAC-SHA-256 #1",
+    "",
+    "",
+    {0xb6, 0x13, 0x67, 0x9a, 0x08, 0x14, 0xd9, 0xec,
+     0x77, 0x2f, 0x95, 0xd7, 0x78, 0xc3, 0x5f, 0xc5,
+     0xff, 0x16, 0x97, 0xc4, 0x93, 0x71, 0x56, 0x53,
+     0xc6, 0xc7, 0x12, 0x14, 0x42, 0x92, 0xc5, 0xad}
+};
+static TestHashVector const testVectorHMAC_SHA256_2 = {
+    "HMAC-SHA-256 #2",
+    "key",
+    "The quick brown fox jumps over the lazy dog",
+    {0xf7, 0xbc, 0x83, 0xf4, 0x30, 0x53, 0x84, 0x24,
+     0xb1, 0x32, 0x98, 0xe6, 0xaa, 0x6f, 0xb1, 0x43,
+     0xef, 0x4d, 0x59, 0xa1, 0x49, 0x46, 0x17, 0x59,
+     0x97, 0x47, 0x9d, 0xbc, 0x2d, 0x1a, 0x3c, 0xd8}
+};
 
 SHA256 sha256;
 
@@ -102,6 +124,86 @@ void testHash(Hash *hash, const struct TestHashVector *test)
         Serial.println("Failed");
 }
 
+// Very simple method for hashing a HMAC inner or outer key.
+void hashKey(Hash *hash, const uint8_t *key, size_t keyLen, uint8_t pad)
+{
+    size_t posn;
+    uint8_t buf;
+    uint8_t result[HASH_SIZE];
+    if (keyLen <= BLOCK_SIZE) {
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < keyLen)
+                buf = key[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    } else {
+        hash->reset();
+        hash->update(key, keyLen);
+        hash->finalize(result, HASH_SIZE);
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < HASH_SIZE)
+                buf = result[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    }
+}
+
+void testHMAC(Hash *hash, size_t keyLen)
+{
+    uint8_t result[HASH_SIZE];
+
+    Serial.print("HMAC-SHA-256 keysize=");
+    Serial.print(keyLen);
+    Serial.print(" ... ");
+
+    // Construct the expected result with a simple HMAC implementation.
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x36);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    hash->finalize(result, HASH_SIZE);
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x5C);
+    hash->update(result, HASH_SIZE);
+    hash->finalize(result, HASH_SIZE);
+
+    // Now use the library to compute the HMAC.
+    hash->resetHMAC(buffer, keyLen);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hash->finalizeHMAC(buffer, keyLen, buffer, HASH_SIZE);
+
+    // Check the result.
+    if (!memcmp(result, buffer, HASH_SIZE))
+        Serial.println("Passed");
+    else
+        Serial.println("Failed");
+}
+
+void testHMAC(Hash *hash, const struct TestHashVector *test)
+{
+    uint8_t result[HASH_SIZE];
+
+    Serial.print(test->name);
+    Serial.print(" ... ");
+
+    hash->resetHMAC(test->key, strlen(test->key));
+    hash->update(test->data, strlen(test->data));
+    hash->finalizeHMAC(test->key, strlen(test->key), result, sizeof(result));
+
+    if (!memcmp(result, test->hash, HASH_SIZE))
+        Serial.println("Passed");
+    else
+        Serial.println("Failed");
+}
+
 void perfHash(Hash *hash)
 {
     unsigned long start;
@@ -135,6 +237,14 @@ void setup()
     Serial.println("Test Vectors:");
     testHash(&sha256, &testVectorSHA256_1);
     testHash(&sha256, &testVectorSHA256_2);
+    testHMAC(&sha256, &testVectorHMAC_SHA256_1);
+    testHMAC(&sha256, &testVectorHMAC_SHA256_2);
+    testHMAC(&sha256, (size_t)0);
+    testHMAC(&sha256, 1);
+    testHMAC(&sha256, HASH_SIZE);
+    testHMAC(&sha256, BLOCK_SIZE);
+    testHMAC(&sha256, BLOCK_SIZE + 1);
+    testHMAC(&sha256, sizeof(buffer));
 
     Serial.println();
 
diff --git a/libraries/Crypto/examples/TestSHA3_256/TestSHA3_256.ino b/libraries/Crypto/examples/TestSHA3_256/TestSHA3_256.ino
index 0619c9b6..527fe097 100644
--- a/libraries/Crypto/examples/TestSHA3_256/TestSHA3_256.ino
+++ b/libraries/Crypto/examples/TestSHA3_256/TestSHA3_256.ino
@@ -31,6 +31,7 @@ correct behaviour.
 
 #define DATA_SIZE 136
 #define HASH_SIZE 32
+#define BLOCK_SIZE 136
 
 struct TestHashVector
 {
@@ -95,7 +96,7 @@ static TestHashVector const testVectorSHA3_256_4 = {
      0xBE, 0x9B, 0x7C, 0x73, 0x6B, 0x80, 0x59, 0xAB,
      0xFD, 0x67, 0x79, 0xAC, 0x35, 0xAC, 0x81, 0xB5}
 };
-static TestHashVector const testVectorSHA3_256_5 = {
+static TestHashVector testVectorSHA3_256_5 = {
     "SHA3-256 #5",
     {0xB3, 0x2D, 0x95, 0xB0, 0xB9, 0xAA, 0xD2, 0xA8,
      0x81, 0x6D, 0xE6, 0xD0, 0x6D, 0x1F, 0x86, 0x00,
@@ -123,8 +124,6 @@ static TestHashVector const testVectorSHA3_256_5 = {
 
 SHA3_256 sha3_256;
 
-byte buffer[128];
-
 bool testHash_N(Hash *hash, const struct TestHashVector *test, size_t inc)
 {
     size_t size = test->dataSize;
@@ -176,25 +175,92 @@ void perfHash(Hash *hash)
     unsigned long start;
     unsigned long elapsed;
     int count;
+    // Reuse one of the test vectors as a large temporary buffer.
+    uint8_t *buffer = (uint8_t *)&testVectorSHA3_256_5;
 
     Serial.print("Hashing ... ");
 
-    for (size_t posn = 0; posn < sizeof(buffer); ++posn)
+    for (size_t posn = 0; posn < 128; ++posn)
         buffer[posn] = (uint8_t)posn;
 
     hash->reset();
     start = micros();
     for (count = 0; count < 500; ++count) {
-        hash->update(buffer, sizeof(buffer));
+        hash->update(buffer, 128);
     }
     elapsed = micros() - start;
 
-    Serial.print(elapsed / (sizeof(buffer) * 500.0));
+    Serial.print(elapsed / (128 * 500.0));
     Serial.print("us per byte, ");
-    Serial.print((sizeof(buffer) * 500.0 * 1000000.0) / elapsed);
+    Serial.print((128 * 500.0 * 1000000.0) / elapsed);
     Serial.println(" bytes per second");
 }
 
+// Very simple method for hashing a HMAC inner or outer key.
+void hashKey(Hash *hash, const uint8_t *key, size_t keyLen, uint8_t pad)
+{
+    size_t posn;
+    uint8_t buf;
+    uint8_t result[HASH_SIZE];
+    if (keyLen <= BLOCK_SIZE) {
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < keyLen)
+                buf = key[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    } else {
+        hash->reset();
+        hash->update(key, keyLen);
+        hash->finalize(result, HASH_SIZE);
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < HASH_SIZE)
+                buf = result[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    }
+}
+
+void testHMAC(Hash *hash, size_t keyLen)
+{
+    uint8_t result[HASH_SIZE];
+    // Reuse one of the test vectors as a large temporary buffer.
+    uint8_t *buffer = (uint8_t *)&testVectorSHA3_256_5;
+
+    Serial.print("HMAC-SHA3-256 keysize=");
+    Serial.print(keyLen);
+    Serial.print(" ... ");
+
+    // Construct the expected result with a simple HMAC implementation.
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x36);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    hash->finalize(result, HASH_SIZE);
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x5C);
+    hash->update(result, HASH_SIZE);
+    hash->finalize(result, HASH_SIZE);
+
+    // Now use the library to compute the HMAC.
+    hash->resetHMAC(buffer, keyLen);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hash->finalizeHMAC(buffer, keyLen, buffer, HASH_SIZE);
+
+    // Check the result.
+    if (!memcmp(result, buffer, HASH_SIZE))
+        Serial.println("Passed");
+    else
+        Serial.println("Failed");
+}
+
 void setup()
 {
     Serial.begin(9600);
@@ -207,6 +273,12 @@ void setup()
     testHash(&sha3_256, &testVectorSHA3_256_3);
     testHash(&sha3_256, &testVectorSHA3_256_4);
     testHash(&sha3_256, &testVectorSHA3_256_5);
+    testHMAC(&sha3_256, (size_t)0);
+    testHMAC(&sha3_256, 1);
+    testHMAC(&sha3_256, HASH_SIZE);
+    testHMAC(&sha3_256, BLOCK_SIZE);
+    testHMAC(&sha3_256, BLOCK_SIZE + 1);
+    testHMAC(&sha3_256, BLOCK_SIZE + 2);
 
     Serial.println();
 
diff --git a/libraries/Crypto/examples/TestSHA3_512/TestSHA3_512.ino b/libraries/Crypto/examples/TestSHA3_512/TestSHA3_512.ino
index 4e18a0f3..8a6381dd 100644
--- a/libraries/Crypto/examples/TestSHA3_512/TestSHA3_512.ino
+++ b/libraries/Crypto/examples/TestSHA3_512/TestSHA3_512.ino
@@ -31,6 +31,7 @@ correct behaviour.
 
 #define DATA_SIZE 72
 #define HASH_SIZE 64
+#define BLOCK_SIZE 72
 
 struct TestHashVector
 {
@@ -199,6 +200,69 @@ void perfHash(Hash *hash)
     Serial.println(" bytes per second");
 }
 
+// Very simple method for hashing a HMAC inner or outer key.
+void hashKey(Hash *hash, const uint8_t *key, size_t keyLen, uint8_t pad)
+{
+    size_t posn;
+    uint8_t buf;
+    uint8_t result[HASH_SIZE];
+    if (keyLen <= BLOCK_SIZE) {
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < keyLen)
+                buf = key[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    } else {
+        hash->reset();
+        hash->update(key, keyLen);
+        hash->finalize(result, HASH_SIZE);
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < HASH_SIZE)
+                buf = result[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    }
+}
+
+void testHMAC(Hash *hash, size_t keyLen)
+{
+    uint8_t result[HASH_SIZE];
+
+    Serial.print("HMAC-SHA3-512 keysize=");
+    Serial.print(keyLen);
+    Serial.print(" ... ");
+
+    // Construct the expected result with a simple HMAC implementation.
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x36);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    hash->finalize(result, HASH_SIZE);
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x5C);
+    hash->update(result, HASH_SIZE);
+    hash->finalize(result, HASH_SIZE);
+
+    // Now use the library to compute the HMAC.
+    hash->resetHMAC(buffer, keyLen);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hash->finalizeHMAC(buffer, keyLen, buffer, HASH_SIZE);
+
+    // Check the result.
+    if (!memcmp(result, buffer, HASH_SIZE))
+        Serial.println("Passed");
+    else
+        Serial.println("Failed");
+}
+
 void setup()
 {
     Serial.begin(9600);
@@ -211,6 +275,12 @@ void setup()
     testHash(&sha3_512, &testVectorSHA3_512_3);
     testHash(&sha3_512, &testVectorSHA3_512_4);
     testHash(&sha3_512, &testVectorSHA3_512_5);
+    testHMAC(&sha3_512, (size_t)0);
+    testHMAC(&sha3_512, 1);
+    testHMAC(&sha3_512, HASH_SIZE);
+    testHMAC(&sha3_512, BLOCK_SIZE);
+    testHMAC(&sha3_512, BLOCK_SIZE + 1);
+    testHMAC(&sha3_512, sizeof(buffer));
 
     Serial.println();
 
diff --git a/libraries/Crypto/examples/TestSHA512/TestSHA512.ino b/libraries/Crypto/examples/TestSHA512/TestSHA512.ino
index e1876459..042598ad 100644
--- a/libraries/Crypto/examples/TestSHA512/TestSHA512.ino
+++ b/libraries/Crypto/examples/TestSHA512/TestSHA512.ino
@@ -29,6 +29,7 @@ This example runs tests on the SHA512 implementation to verify correct behaviour
 #include <string.h>
 
 #define HASH_SIZE 64
+#define BLOCK_SIZE 128
 
 struct TestHashVector
 {
@@ -77,7 +78,7 @@ static TestHashVector const testVectorSHA512_3 = {
 
 SHA512 sha512;
 
-byte buffer[128];
+byte buffer[BLOCK_SIZE + 2];
 
 bool testHash_N(Hash *hash, const struct TestHashVector *test, size_t inc)
 {
@@ -147,6 +148,69 @@ void perfHash(Hash *hash)
     Serial.println(" bytes per second");
 }
 
+// Very simple method for hashing a HMAC inner or outer key.
+void hashKey(Hash *hash, const uint8_t *key, size_t keyLen, uint8_t pad)
+{
+    size_t posn;
+    uint8_t buf;
+    uint8_t result[HASH_SIZE];
+    if (keyLen <= BLOCK_SIZE) {
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < keyLen)
+                buf = key[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    } else {
+        hash->reset();
+        hash->update(key, keyLen);
+        hash->finalize(result, HASH_SIZE);
+        hash->reset();
+        for (posn = 0; posn < BLOCK_SIZE; ++posn) {
+            if (posn < HASH_SIZE)
+                buf = result[posn] ^ pad;
+            else
+                buf = pad;
+            hash->update(&buf, 1);
+        }
+    }
+}
+
+void testHMAC(Hash *hash, size_t keyLen)
+{
+    uint8_t result[HASH_SIZE];
+
+    Serial.print("HMAC-SHA-512 keysize=");
+    Serial.print(keyLen);
+    Serial.print(" ... ");
+
+    // Construct the expected result with a simple HMAC implementation.
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x36);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    hash->finalize(result, HASH_SIZE);
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hashKey(hash, buffer, keyLen, 0x5C);
+    hash->update(result, HASH_SIZE);
+    hash->finalize(result, HASH_SIZE);
+
+    // Now use the library to compute the HMAC.
+    hash->resetHMAC(buffer, keyLen);
+    memset(buffer, 0xBA, sizeof(buffer));
+    hash->update(buffer, sizeof(buffer));
+    memset(buffer, (uint8_t)keyLen, keyLen);
+    hash->finalizeHMAC(buffer, keyLen, buffer, HASH_SIZE);
+
+    // Check the result.
+    if (!memcmp(result, buffer, HASH_SIZE))
+        Serial.println("Passed");
+    else
+        Serial.println("Failed");
+}
+
 void setup()
 {
     Serial.begin(9600);
@@ -157,6 +221,12 @@ void setup()
     testHash(&sha512, &testVectorSHA512_1);
     testHash(&sha512, &testVectorSHA512_2);
     testHash(&sha512, &testVectorSHA512_3);
+    testHMAC(&sha512, (size_t)0);
+    testHMAC(&sha512, 1);
+    testHMAC(&sha512, HASH_SIZE);
+    testHMAC(&sha512, BLOCK_SIZE);
+    testHMAC(&sha512, BLOCK_SIZE + 1);
+    testHMAC(&sha512, BLOCK_SIZE + 2);
 
     Serial.println();