diff --git a/flash-ipmi.cpp b/flash-ipmi.cpp
index daaab5e..ab294c3 100644
--- a/flash-ipmi.cpp
+++ b/flash-ipmi.cpp
@@ -55,3 +55,9 @@
     /* TODO: implement. */
     return false;
 }
+
+bool FlashUpdate::hashData(uint32_t offset, const std::vector<uint8_t>& bytes)
+{
+    /* TODO: implement. */
+    return false;
+}
diff --git a/flash-ipmi.hpp b/flash-ipmi.hpp
index 7a63fc3..ddcfa14 100644
--- a/flash-ipmi.hpp
+++ b/flash-ipmi.hpp
@@ -114,6 +114,16 @@
      * @return true on success, false otherwise.
      */
     virtual bool startHash(uint32_t length) = 0;
+
+    /**
+     * Attempt to write the bytes at the offset.
+     *
+     * @param[in] offset - the 0-based byte offset into the flash image.
+     * @param[in] bytes - the bytes to write.
+     * @return true on success, false otherwise.
+     */
+    virtual bool hashData(uint32_t offset,
+                          const std::vector<uint8_t>& bytes) = 0;
 };
 
 class FlashUpdate : public UpdateInterface
@@ -127,12 +137,11 @@
     FlashUpdate& operator=(FlashUpdate&&) = default;
 
     bool start(uint32_t length) override;
-
     bool flashData(uint32_t offset, const std::vector<uint8_t>& bytes) override;
-
     bool flashFinish() override;
 
     bool startHash(uint32_t length) override;
+    bool hashData(uint32_t offset, const std::vector<uint8_t>& bytes) override;
 
   private:
     /**
diff --git a/ipmi.cpp b/ipmi.cpp
index 00f027a..50208d3 100644
--- a/ipmi.cpp
+++ b/ipmi.cpp
@@ -26,6 +26,7 @@
         {FlashSubCmds::flashStartTransfer, sizeof(struct StartTx)},
         {FlashSubCmds::flashDataBlock, sizeof(struct ChunkHdr) + 1},
         {FlashSubCmds::flashStartHash, sizeof(struct StartTx)},
+        {FlashSubCmds::flashHashData, sizeof(struct ChunkHdr) + 1},
     };
 
     auto results = minimumLengths.find(command);
@@ -66,10 +67,10 @@
     struct ChunkHdr hdr;
     std::memcpy(&hdr, reqBuf, sizeof(hdr));
 
-    size_t requestLength = (*dataLen);
+    auto requestLength = *dataLen;
 
     /* Grab the bytes from the packet. */
-    size_t bytesLength = requestLength - sizeof(struct ChunkHdr);
+    auto bytesLength = requestLength - sizeof(struct ChunkHdr);
     std::vector<uint8_t> bytes(bytesLength);
     std::memcpy(bytes.data(), &reqBuf[sizeof(struct ChunkHdr)], bytesLength);
 
@@ -115,3 +116,29 @@
     (*dataLen) = 1;
     return IPMI_CC_OK;
 }
+
+ipmi_ret_t hashBlock(UpdateInterface* updater, const uint8_t* reqBuf,
+                     uint8_t* replyBuf, size_t* dataLen)
+{
+    struct ChunkHdr hdr;
+    std::memcpy(&hdr, reqBuf, sizeof(hdr));
+
+    auto requestLength = *dataLen;
+
+    /* Grab the bytes from the packet. */
+    auto bytesLength = requestLength - sizeof(struct ChunkHdr);
+    std::vector<uint8_t> bytes(bytesLength);
+    std::memcpy(bytes.data(), &reqBuf[sizeof(struct ChunkHdr)], bytesLength);
+
+    /* TODO: Refactor this and dataBlock for re-use. */
+
+    if (!updater->hashData(hdr.offset, bytes))
+    {
+        return IPMI_CC_INVALID;
+    }
+
+    /* We were successful and set the response byte to 0. */
+    replyBuf[0] = 0x00;
+    (*dataLen) = 1;
+    return IPMI_CC_OK;
+}
diff --git a/ipmi.hpp b/ipmi.hpp
index e80c68e..1010b6f 100644
--- a/ipmi.hpp
+++ b/ipmi.hpp
@@ -64,3 +64,16 @@
  */
 ipmi_ret_t startHash(UpdateInterface* updater, const uint8_t* reqBuf,
                      uint8_t* replyBuf, size_t* dataLen);
+
+/**
+ * Receive a flash hash data block and store it.
+ *
+ * @param[in] updater - Pointer to Updater object.
+ * @param[in] reqBuf - the IPMI packet.
+ * @param[in] replyBuf - Pointer to buffer for any response.
+ * @param[in,out] dataLen - Initially reqBuf length, set to replyBuf
+ * length when done.
+ * @return corresponding IPMI return code.
+ */
+ipmi_ret_t hashBlock(UpdateInterface* updater, const uint8_t* reqBuf,
+                     uint8_t* replyBuf, size_t* dataLen);
diff --git a/main.cpp b/main.cpp
index d56fed5..cb86fcd 100644
--- a/main.cpp
+++ b/main.cpp
@@ -69,6 +69,9 @@
         case FlashSubCmds::flashStartHash:
             return startHash(flashUpdateSingleton.get(), reqBuf, replyCmdBuf,
                              dataLen);
+        case FlashSubCmds::flashHashData:
+            return hashBlock(flashUpdateSingleton.get(), reqBuf, replyCmdBuf,
+                             dataLen);
         default:
             return IPMI_CC_INVALID;
     }
diff --git a/test/Makefile.am b/test/Makefile.am
index 282a824..392db5c 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -14,6 +14,7 @@
 	ipmi_flashdata_unittest \
 	ipmi_flashfinish_unittest \
 	ipmi_starthash_unittest \
+	ipmi_hashdata_unittest \
 	ipmi_validate_unittest
 
 TESTS = $(check_PROGRAMS)
@@ -30,5 +31,8 @@
 ipmi_starthash_unittest_SOURCES = ipmi_starthash_unittest.cpp
 ipmi_starthash_unittest_LDADD = $(top_builddir)/ipmi.o
 
+ipmi_hashdata_unittest_SOURCES = ipmi_hashdata_unittest.cpp
+ipmi_hashdata_unittest_LDADD = $(top_builddir)/ipmi.o
+
 ipmi_validate_unittest_SOURCES = ipmi_validate_unittest.cpp
 ipmi_validate_unittest_LDADD = $(top_builddir)/ipmi.o
diff --git a/test/ipmi_hashdata_unittest.cpp b/test/ipmi_hashdata_unittest.cpp
new file mode 100644
index 0000000..17de66c
--- /dev/null
+++ b/test/ipmi_hashdata_unittest.cpp
@@ -0,0 +1,43 @@
+#include "flash-ipmi.hpp"
+#include "ipmi.hpp"
+
+#include "updater_mock.hpp"
+
+#include <cstring>
+#include <gtest/gtest.h>
+
+using ::testing::ElementsAreArray;
+using ::testing::Return;
+using ::testing::StrictMock;
+
+// ipmid.hpp isn't installed where we can grab it and this value is per BMC
+// SoC.
+#define MAX_IPMI_BUFFER 64
+
+TEST(IpmiHashData, DataReceivedIsPassedOnOk)
+{
+    // If valid data was passed in, it'll pass it onto the update handler.
+
+    StrictMock<UpdaterMock> updater;
+
+    size_t dataLen;
+    uint8_t request[MAX_IPMI_BUFFER] = {0};
+    uint8_t reply[MAX_IPMI_BUFFER] = {0};
+
+    struct ChunkHdr tx;
+    tx.cmd = FlashSubCmds::flashHashData;
+    tx.offset = 0x00;
+    std::memcpy(request, &tx, sizeof(tx));
+
+    uint8_t bytes[] = {0x04, 0x05};
+    std::memcpy(&request[sizeof(struct ChunkHdr)], bytes, sizeof(bytes));
+
+    dataLen = sizeof(struct ChunkHdr) + sizeof(bytes);
+
+    EXPECT_CALL(updater, hashData(0x00, ElementsAreArray(bytes, sizeof(bytes))))
+        .WillOnce(Return(true));
+
+    EXPECT_EQ(IPMI_CC_OK, hashBlock(&updater, request, reply, &dataLen));
+    EXPECT_EQ(sizeof(uint8_t), dataLen);
+    EXPECT_EQ(0, reply[0]);
+}
diff --git a/test/ipmi_validate_unittest.cpp b/test/ipmi_validate_unittest.cpp
index be4b128..14ada91 100644
--- a/test/ipmi_validate_unittest.cpp
+++ b/test/ipmi_validate_unittest.cpp
@@ -41,8 +41,15 @@
 TEST(IpmiValidateTest, StartHashInvalidReturnsFalse)
 {
     // Verify the request is sanity checked w.r.t length.
-
     auto cmd = FlashSubCmds::flashStartHash;
     size_t dataLen = sizeof(struct StartTx) - 1;
     EXPECT_FALSE(validateRequestLength(cmd, dataLen));
 }
+
+TEST(IpmiValidateTest, InvalidLengthHashBlockReturnsFalse)
+{
+    // This request isn't large enough to be well-formed.
+    auto cmd = FlashSubCmds::flashHashData;
+    size_t dataLen = sizeof(struct ChunkHdr) - 1;
+    EXPECT_FALSE(validateRequestLength(cmd, dataLen));
+}
diff --git a/test/updater_mock.hpp b/test/updater_mock.hpp
index 561deaa..1e03a31 100644
--- a/test/updater_mock.hpp
+++ b/test/updater_mock.hpp
@@ -14,4 +14,5 @@
     MOCK_METHOD2(flashData, bool(uint32_t, const std::vector<uint8_t>&));
     MOCK_METHOD0(flashFinish, bool());
     MOCK_METHOD1(startHash, bool(uint32_t));
+    MOCK_METHOD2(hashData, bool(uint32_t, const std::vector<uint8_t>&));
 };