diff --git a/src/core/libs/osnma_msg_receiver.cc b/src/core/libs/osnma_msg_receiver.cc
index 8f157414f..cf7e3adc9 100644
--- a/src/core/libs/osnma_msg_receiver.cc
+++ b/src/core/libs/osnma_msg_receiver.cc
@@ -416,8 +416,7 @@ void osnma_msg_receiver::process_dsm_message(const std::vector<uint8_t>& dsm_msg
                               << ", TOW=" << static_cast<uint32_t>(d_osnma_data.d_dsm_kroot_message.towh_k) * 3600
                               << " received" << std::endl;
                     // C: NPK verification against Merkle tree root.
-                    std::vector<uint8_t> m_0;
-                    d_public_key_verified = verify_dsm_pkr(d_osnma_data.d_dsm_pkr_message, m_0);
+                    d_public_key_verified = verify_dsm_pkr(d_osnma_data.d_dsm_pkr_message);
                 }
         }
     else
@@ -735,10 +734,49 @@ void osnma_msg_receiver::process_mack_message(const std::shared_ptr<OSNMA_msg>&
     // C: TODO - where m = (PRNd || PRNa || GSTsf || CTR || NMAS || NavData || P)
 }
 
-bool osnma_msg_receiver::verify_dsm_pkr(DSM_PKR_message message, std::vector<uint8_t> m0)
+bool osnma_msg_receiver::verify_dsm_pkr(DSM_PKR_message message)
 {
-    // TODO concatenate message
+    // TODO create leafe base message m_i
     // TODO create function for recursively apply hash
 
-    return false;
+    // build base leaf m_i
+//    auto leaf = message.mid;
+    std::vector<uint8_t> m_i;
+    m_i.reserve(2 + message.npk.size());
+    m_i[0] = message.npkt;
+    m_i[1] = message.npktid;
+    for (uint8_t i = 2; i < m_i.size(); i++)
+        {
+            m_i.push_back(message.npk[i]);
+        }
+
+    // compute intermediate leafs' values
+    std::vector<uint8_t> x_0,x_1,x_2,x_3,x_4;
+//    uint8_t  k = 0;
+    x_0 = d_crypto->computeSHA256(m_i);
+    x_0.insert(x_0.end(),message.itn.begin(),&message.itn[31]);
+    x_1 = d_crypto->computeSHA256(x_0);
+    x_1.insert(x_1.end(),&message.itn[32],&message.itn[63]);
+    x_2 = d_crypto->computeSHA256(x_1);
+    x_2.insert(x_2.end(),&message.itn[64],&message.itn[95]);
+    x_3 = d_crypto->computeSHA256(x_2);
+    x_3.insert(x_3.end(),&message.itn[96],&message.itn[127]);
+    // root leaf computation
+    x_4 = d_crypto->computeSHA256(x_3);
+
+    // C: d_crypto->getMerkleRoot([m_0:m_15]) I realised I could have done this...
+    // C: ... but why computing all the possible results?  I have only one leaf in each osnma message...
+    // verify that computed root matches merkle root
+
+    if(x_4 == d_crypto->getMerkleRoot())
+        {
+            std::cout << "Galileo OSNMA: DSM-PKR verified successfully! " << std::endl;
+            return true;
+            // C: NPK verification against Merkle tree root.
+        }
+    else
+        {
+            std::cout << "Galileo OSNMA: DSM-PKR verification unsuccessful !" << std::endl;
+            return false;
+        }
 }
diff --git a/src/core/libs/osnma_msg_receiver.h b/src/core/libs/osnma_msg_receiver.h
index 89522bc69..2c9cedcc7 100644
--- a/src/core/libs/osnma_msg_receiver.h
+++ b/src/core/libs/osnma_msg_receiver.h
@@ -65,7 +65,7 @@ private:
     void read_dsm_header(uint8_t dsm_header);
     void read_dsm_block(const std::shared_ptr<OSNMA_msg>& osnma_msg);
     void process_dsm_message(const std::vector<uint8_t>& dsm_msg, const std::shared_ptr<OSNMA_msg>& osnma_msg);
-    bool verify_dsm_pkr(DSM_PKR_message message, std::vector<uint8_t> input_message);
+    bool verify_dsm_pkr(DSM_PKR_message message);
     void read_mack_block(const std::shared_ptr<OSNMA_msg>& osnma_msg);
     void read_mack_header();
     void read_mack_body();
diff --git a/src/core/system_parameters/gnss_crypto.h b/src/core/system_parameters/gnss_crypto.h
index c544020a9..50047c440 100644
--- a/src/core/system_parameters/gnss_crypto.h
+++ b/src/core/system_parameters/gnss_crypto.h
@@ -50,6 +50,10 @@ public:
     void readPublicKeyFromPEM(const std::string& pemFilePath);
     void read_merkle_xml(const std::string& merkleFilePath);
     std::vector<uint8_t> getMerkleRoot(const std::vector<std::vector<uint8_t>>& merkle) const;
+    std::vector<uint8_t> getMerkleRoot() const
+    {
+        return d_x_4_0;
+    }
 
     // void set_public_key(const std::vector<uint8_t>& publickey);