CBC blood test Information | Mount Sinai

Complete blood count; Anemia – CBC

A complete blood count (CBC) test measures the following:

• The number of white blood cells (WBC count)
• The number of red blood cells (RBC count)
• The number of platelets
• The total amount of hemoglobin in the blood
• The fraction of the blood composed of red blood cells (hematocrit)

The CBC test also provides information about the following measurements:

• Mean red blood cell volume (MCV)
• Mean hemoglobin amount per red blood cell (MCH)
• The mean amount of hemoglobin relative to the size of the cell (hemoglobin concentration) per red blood cell (MCHC)

The complete blood count (CBC) is test, used to diagnose and monitor numerous diseases. It can reflect problems with fluid volume (such as dehydration) or loss of blood. It can show abnormalities in the production, life span, and destruction of blood cells. It can reflect acute or chronic infection, allergies, and problems with clotting. The CBC test identifies and counts the 7 types of cells found in the blood, red blood cell, neutrophil, eosinophil, basophil, lymphocyte, monocyte, and platelet.

Sickle cell anemia is an inherited blood disease in which the red blood cells produce abnormal pigment (hemoglobin). The abnormal hemoglobin causes deformity of the red blood cells into crescent or sickle-shapes, as seen in this photomicrograph.

This picture shows large, dense, oversized, red blood cells (RBCs) that are seen in megaloblastic anemia. Megaloblastic anemia can occur when there is a deficiency of vitamin B-12.

This photomicrograph shows one of the abnormal shapes that red blood cells (RBCs) may assume, a tear-drop shape. Normally, RBCs are round.

This photomicrograph shows normal red blood cells (RBCs) as seen in the microscope after staining.

Elliptocytosis is a hereditary disorder of the red blood cells (RBCs). In this condition, the RBCs assume an elliptical shape, rather than the typical round shape.

Spherocytosis is a hereditary disorder of the red blood cells (RBCs), which may be associated with a mild anemia. Typically, the affected RBCs are small, spherically shaped, and lack the light centers seen in normal, round RBCs.

Sickle cell anemia is an inherited disorder in which abnormal hemoglobin (the red pigment inside red blood cells) is produced. The abnormal hemoglobin causes red blood cells to assume a sickle shape, like the ones seen in this photomicrograph.

Basophils are a specific type of white blood cell. These cells are readily stained with basic dyes (this is where the name comes from). Note the dark grains inside the cellular fluid (cytoplasm) of this basophil. Basophils make up only a small portion of the number of white blood cells but are important parts of the body’s immune response. They release histamine and other chemicals that act on the blood vessels when the immune response is triggered.

Malarial parasites are visible within the red blood cells. They are stained a dark bluish color.

Malaria is a disease caused by parasites. This picture shows dark orange-stained malaria parasites inside red blood cells (a) and outside the cells (b). Note the large cells that look like targets; it is unknown how these target cells are related to this disease.

These crescent or sickle-shaped red blood cells (RBCs) are present with Sickle cell anemia, and stand out clearly against the normal round RBCs. These abnormally shaped cells may become entangled and block blood flow in the small blood vessels (capillaries).

This photomicrograph of red blood cells (RBCs) shows both sickle-shaped and Pappenheimer bodies.

These abnormal red blood cells (RBCs) resemble targets. These cells are seen in association with some forms of anemia, and following the removal of the spleen (splenectomy).

Blood transports oxygen and nutrients to body tissues and returns waste and carbon dioxide. Blood distributes nearly everything that is carried from one area in the body to another place within the body. For example, blood transports hormones from endocrine organs to their target organs and tissues. Blood helps maintain body temperature and normal pH levels in body tissues. The protective functions of blood include clot formation and the prevention of infection.

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

There is no special preparation needed.

How the Test will Feel

When the needle is inserted to draw blood, you may feel moderate pain. Some people feel only a prick or stinging. Afterward there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

A CBC is a commonly performed lab test. It can be used to detect or monitor many different health conditions. Your health care provider may order this test:

• If you are having symptoms, such as fatigue, weight loss, fever or other signs of an infection, weakness, bruising, bleeding, or any signs of cancer
• When you are receiving treatments (medicines or radiation) that may change your blood count results
• To monitor a long-term (chronic) health problem that may change your blood count results, such as chronic kidney disease

Normal Results

Blood counts may vary with altitude. In general, normal results are:

RBC count:

• Male: 4.7 to 6.1 million cells/mcL
• Female: 4.2 to 5.4 million cells/mcL

WBC count:

• 4,500 to 10,000 cells/mcL

Hematocrit:

• Male: 40. 7% to 50.3%
• Female: 36.1% to 44.3%

Hemoglobin:

• Male: 13.8 to 17.2 gm/dL
• Female: 12.1 to 15.1 gm/dL

Red blood cell indices:

• MCV: 80 to 95 femtoliter
• MCH: 27 to 31 pg/cell
• MCHC: 32 to 36 gm/dL

Platelet count:

• 150,000 to 450,000/dL

The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean

High RBC, hemoglobin, or hematocrit may be due to:

• A lack of enough water and fluids, such as from severe diarrhea, excessive sweating, or water pills used to treat high blood pressure
• Kidney disease with high erythropoietin production
• Low oxygen level in the blood for a long time, most often due to heart or lung disease, chronic carbon monoxide exposure, or living at a high altitude
• Polycythemia vera
• Smoking
• Use of testosterone

Low RBC, hemoglobin, or hematocrit is a sign of anemia, which can result from:

• Blood loss (either sudden, or from problems such as heavy menstrual periods over a long time)
• Bone marrow failure (for example, from radiation, infection, or tumor)
• Breakdown of red blood cells (hemolysis)
• Cancer and cancer treatment
• Certain long-term (chronic) medical conditions, such as chronic kidney disease, ulcerative colitis, or rheumatoid arthritis
• Iron deficiency
• Leukemia
• Long-term infections such as hepatitis
• Poor diet and nutrition, causing too little iron, folate, vitamin B12, or vitamin B6
• Multiple myeloma

A lower than normal white blood cell count is called leukopenia. A decreased WBC count may be due to:

• Alcohol abuse and liver damage
• Autoimmune diseases (such as systemic lupus erythematosus)
• Bone marrow failure (for example, due to infection, tumor, radiation, or fibrosis)
• Chemotherapy medicines used to treat cancer
• Disease of the liver or spleen
• Enlarged spleen
• Infections caused by viruses, such as mono or AIDS
• Medicines

A high WBC count is called leukocytosis. It can result from:

• Certain medicines, such as corticosteroids
• Infections
• Diseases such as lupus, rheumatoid arthritis, or allergy
• Leukemia
• Severe emotional or physical stress
• Tissue damage (such as from burns or a heart attack)

A high platelet count may be due to:

• Bleeding
• Diseases such as cancer or blood disease
• Iron deficiency
• Problems with the bone marrow

A low platelet count may be due to:

• Disorders where platelets are destroyed
• Pregnancy
• Enlarged spleen
• Bone marrow failure (for example, due to infection, tumor, radiation, or fibrosis)
• Chemotherapy medicines used to treat cancer

Risks

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Considerations

RBCs transport hemoglobin which, in turn, carries oxygen. The amount of oxygen received by body tissues depends on the amount and function of RBCs and hemoglobin.

WBCs are mediators of inflammation and the immune response. There are various types of WBCs that normally appear in the blood:

• Neutrophils (polymorphonuclear leukocytes)
• Band cells (slightly immature neutrophils)
• T-type lymphocytes (T cells)
• B-type lymphocytes (B cells)
• Monocytes
• Eosinophils
• Basophils

Lin JC, Benz Jr. EJ. Approach to anemia in the adult and child. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 35.

Means RT. Approach to the anemias. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 149.

Vajpayee N, Graham SS, Bem S. Basic examination of blood and bone marrow. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 31.

Last reviewed on: 10/16/2022

Reviewed by: Mark Levin, MD, Hematologist and Oncologist, Monsey, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

WBC count Information | Mount Sinai

Leukocyte count; White blood cell count; White blood cell differential; WBC differential; Infection – WBC count; Cancer – WBC count

A WBC count is a blood test to measure the number of white blood cells (WBCs) in the blood. It is a part of a complete blood count (CBC).

WBCs are also called leukocytes. They help fight infections. There are five major types of white blood cells:

• Basophils
• Eosinophils
• Lymphocytes (T cells, B cells, and Natural Killer cells)
• Monocytes
• Neutrophils

Basophils are a specific type of white blood cell. These cells are readily stained with basic dyes (this is where the name comes from). Note the dark grains inside the cellular fluid (cytoplasm) of this basophil. Basophils make up only a small portion of the number of white blood cells but are important parts of the body’s immune response. They release histamine and other chemicals that act on the blood vessels when the immune response is triggered.

Blood transports oxygen and nutrients to body tissues and returns waste and carbon dioxide. Blood distributes nearly everything that is carried from one area in the body to another place within the body. For example, blood transports hormones from endocrine organs to their target organs and tissues. Blood helps maintain body temperature and normal pH levels in body tissues. The protective functions of blood include clot formation and the prevention of infection.

The White Blood Cell (WBC) Count measures two components; the total number of WBC’s (leukocytes) and the differential count. The differential count measures the percentages of each type of leukocyte present. WBC’s are composed of granulocytes (neutrophils, eosinophils, and basophils) and non-granulocytes (lymphocytes and monocytes). White blood cells are a major component of the body’s immune system. Indications for a WBC count include infectious and inflammatory diseases; leukemia and lymphoma; and bone marrow disorders.

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

Most of the time, you do not need to take special steps before this test. Tell your health care provider the medicines you are taking, including the ones without a prescription. Some drugs may change the test results.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

You will have this test to find out how many WBCs you have. Your provider may order this test to help diagnose conditions such as:

• An infection
• Allergic reaction
• Inflammation
• Blood cancer such as leukemia or lymphoma

Normal Results

The normal number of WBCs in the blood is 4,500 to 11,000 WBCs per microliter (4.5 to 11.0 × 10⁹/L).

Normal value ranges may vary slightly among different labs. Some labs use different measurements or may test different specimens. Talk to your provider about your test results.

What Abnormal Results Mean

LOW WBC COUNT

A low number of WBCs is called leukopenia. A count less than 4,500 cells per microliter (4.5 × 10⁹/L) is below normal.

Neutrophils are one type of WBC. They are important for fighting infections.

A lower than normal WBC count may be due to:

• Bone marrow deficiency or failure (for example, due to infection, tumor, or abnormal scarring)
• Cancer treating drugs, or other medicines (see list below)
• Certain autoimmune disorders such as lupus (SLE)
• Disease of the liver or spleen
• Radiation treatment for cancer
• Certain viral illnesses, such as mononucleosis (mono)
• Cancers that damage the bone marrow
• Very severe bacterial infections
• Severe emotional or physical stress (such as from an injury or surgery)
• An ethnic/genetic trait (not uncommon in African Americans)

HIGH WBC COUNT

A higher than normal WBC count is called leukocytosis. It may be due to:

• Certain drugs or medicines (see list below)
• Cigarette smoking
• After spleen removal surgery
• Infections, most often those caused by bacteria
• Inflammatory disease (such as rheumatoid arthritis or allergy)
• Leukemia or Hodgkin disease
• Tissue damage (for example, burns)
• Pregnancy

There may also be less common reasons for abnormal WBC counts.

Drugs that may lower your WBC count include:

• Antibiotics
• Anticonvulsants
• Antithyroid drugs
• Arsenicals
• Captopril
• Chemotherapy drugs
• Chlorpromazine
• Clozapine
• Diuretics (water pills)
• Histamine-2 blockers
• Sulfonamides
• Quinidine
• Terbinafine
• Ticlopidine

Drugs that may increase WBC counts include:

• Beta adrenergic agonists (for example, albuterol)
• Corticosteroids
• Epinephrine
• Granulocyte colony stimulating factor
• Heparin
• Lithium

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Marcogliese AN, Hensch L. Resources for the hematologist: interpretive comments and selected reference values for neonatal, pediatric, and adult populations. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 159.

Vajpayee N, Graham SS, Bem S. Basic examination of blood and bone marrow. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 31.

Last reviewed on: 2/2/2023

Reviewed by: Mark Levin, MD, Hematologist and Oncologist, Monsey, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

Hemogram with leukogram (B-CBC 5-diff, B-CBC 3-diff )

Hemogram with leukogram (B-CBC 5-diff, B-CBC 3-diff ) – SYNLAB Eesti

A hemogram is a comprehensive study in which the content of hemoglobin in the blood is measured, blood cells are counted: leukocytes, erythrocytes, platelets, and erythrocyte and platelet indices are calculated.

Leukogram with 5-component leukogram presented in absolute values:

• neutrophils
• eosinophils
• basophils
• lymphocytes
• monocytes

Leukogram with 3-component leukogram presented in absolute values:

• neutrophils
• lymphocytes
• MXD cells (monocytes, eosinophils, basophils)

Readings:

• Diagnosis of anemia. In addition to measuring hemoglobin and RBC levels, red blood evaluation also considers mean red cell volume (MCV), mean hemoglobin per erythrocyte (MCH), and mean hemoglobin concentration in erythrocyte (MCHC), as well as the red blood cell distribution index by volume (anisocytosis index RDW) .
• Determination of the presence of a pathological process based on changes in the number of leukocytes and in the leukogram, for example, infection, inflammation, allergy, malignancy, immunosuppression,.
• Determination of the platelet count is an important test in the presence of signs of bleeding. A change in the number of platelets, together with the indices characterizing them (MPV – mean platelet volume, PDW – platelet distribution width by volume) indicates a possible disturbance in platelet production or their accelerated destruction.

Analysis method: Flow cytometry

See table for reference values ​​

See table for critical values ​​

Interpretation of the result:

HEMOGLOBIN, HEMATOCRITE, RED CYTES

Normally, the values ​​of hemoglobin, hematocrit and erythrocytes are interconnected and change in the same direction.

• Low values: anemia
• High values: hypovolemia, polycythemia, chronic oxygen deficiency, smoking.

RBC INDICES: MCV, MCH, MCHC, RDW-CV

RBC indices characterize the morphological type of anemia.

Normocytic normochromic (MCV normal, MSI normal):

• Early stage iron deficiency
• Chronic disease (e.g. cancer)
• Acute blood loss
• Aplastic anemia
• Acquired hemolytic anemia (e.g. prosthetic heart valves)

Microcytic hypochromic (MCV ↓, MCH ↓):

• Advanced iron deficiency
• Thalassemia
• Lead poisoning

Microcytic normochromic (MCV ↓, MCH normal):

• Kidney disease (erythropoietin deficiency)

Macrocytic normochromic (MCV ↑, MCH normal):

• Folic acid or vitamin B12 deficiency
• Chemotherapy

Other possible causes of MCV ↑: pregnancy, certain drugs, alcohol.

With significant changes in MCV, it is necessary to evaluate the morphology of erythrocytes in the blood smear preparation.

RDW

Indicates Indicates the variability in RBC volume (anisocytosis).

L LEUKOCYTES, LEUKOGRAM

• There are many possible causes of leukocytosis. More accurate information is given by an automatic 5-component leukogram of 5 types of leukocytes.
• A total white blood cell count that falls within the reference interval does not rule out abnormalities in different white blood cell populations.
• Neutrophilia – acute inflammation, toxic injury, immune disease, myeloproliferative disease.
• Eosinophilia – allergies, parasites, immune syndromes, malignant diseases (lymphoma, carcinoma).
• Basophilia – allergy, myeloproliferative diseases.
• Monocytosis – chronic inflammation, diseases occurring with tissue damage, chronic myeloproliferative diseases.
• Lymphocytosis – viral infections, reactive conditions, malignant lymphoproliferative diseases.
• Leukopenia – usually occurs from neutropenia. Occurs with viral infections, toxic (for example, drugs) or immune damage to the hematopoietic function, and with acute leukemia.

PLATELETS

• Thrombocytopenia most often occurs in connection with viral infections, the use of drugs, some autoimmune diseases, liver diseases, megaloblastic anemia, alcoholism, diseases of the hematopoietic system, hypersplenism.
• So-called pseudothrombocytopenia occurs when several aggregated platelets are counted by the analyzer as one large platelet.
  • This may be due to insufficient mixing of blood with anticoagulant after sample collection or platelet sensitivity to EDEDTA. In this case, to count the platelets, the test should be repeated by taking the blood into the citrate tube used for coagulation tests (with a blue stopper). Platelet aggregates are clearly visible by microscopic examination of a blood smear.
  • Thrombocytosis usually occurs in association with myeloproliferative disorders such as polycythemia and essential thrombocythemia and after splenectomy.
• Elevated platelet values ​​often occur together with reactive changes in leukocytes in bacterial infections.

PLATELET INDICES: MPV, PDW

MPV and PDW are important in clarifying the essence of the nature of thrombocytopenia and thrombocytosis.

• Elevated MRV and thrombocytopenia – indicates a normal regenerative ability of thrombocytopenia.
• Artifact MPV increase:
  • Long time between sample collection and analysis itself – platelets swell in blood sample cells EDTA
  • Platelet aggregates
• High PDW and MPV values ​​are a common finding in chronic myeloproliferative diseases.
• Increased PDW and decreased platelet count are common findings in megaloblastic anemias.
• Normal PDW and platelet count >500 × 109/L – often associated with reactive changes

Indications for blood smear microscopy

If the result of the absolute blood count is one If any of the following indicators are present in the hemogram, and if the analyzer reports atypical morphology, then blood smear microscopy is performed as a clarifying study.

Parameter	Hemogram with 3-component leukogram	Hemogram with 5-component leukogram
Erythrocytes	< 2.0 x 10 12 /L > 6.5 x 10 12 /L	< 2.0 x 1012/L > 6.5 x 1012/L
Hemoglobin	< 80 g/L > 200 g/L	< 80 g/L > 200 g/L
Leukocytes	< 1. 5 x 109/L > 15 x 109/L (> 2 l) > 20 x 109/L (< 2 l) ≤ 2 x 10 9 /L	< 1.5 x 109/L > 15 x 109/L (> 2 l) > 20 x 109/L (< 2 l) ≤ 2 x 10 9 /L
Neutrophils	< 1.0 x 109/L > 20 x 109/L	< 1.0 x 109/L > 20 x 109/L
Lymphocytes	< 0.8 x 109/L > 5.0 x 109/L (> 12 l) > 7.0 x 109/L (< 12 l)	< 0.8 x 109/L > 5.0 x 109/L (> 12 l) > 7.0 x 109/L (< 12 l)
Monocytes		> 1.5 x 109/L (> 12 l) > 3.0 x 109/L (< 12 l)
MXD cells (monocytes, eosinophils, basophils)	> 2 x 109/L (> 12 l) > 3.5 x 109/L (< 12 l)
Platelets	< 100 x 109/L > 1000 x 109/L	< 100 x 109/L > 1000 x 109/L

KNOW INTUIT | Lecture | DES and AES Encryption Algorithms

< Supplementary Material || Lecture 5 : 123

Abstract: One of the most famous private key cryptographic systems is DES – Data Encryption Standard. This system was the first to receive the status of a state standard in the field of data encryption. And although the old American DES standard has now lost its official status, this algorithm still deserves attention when studying cryptography. In addition, this lecture explains what a “double DES” is, a “meet in the middle” attack, and how to fix it. The same lecture briefly discusses the new US block cipher standard, the Rijndael algorithm.

Keywords: DES, IBM, algorithm, commercial information, key length, bit, cipher, computer, personal computer, value, input, data block, branch, data exchange, permutation, loop, whitening, key, subset, value, operations, XOR, result substitution, substitution, security, cryptographic system, algorithm input, decryption, generalization, attack, encryption, byte, ANSI, ISO, proton, international, NIST, AES, advanced, encryption, standard, Rijndael, number of rounds, network, block length, write, redundancy, headers, debugging, CBC, data transformation

intuit.ru/2010/edi”> Lecture aims to introduce the student to the basics of the DES encryption algorithm.

Basic information

One of the best known private key cryptographic systems is DES – Data Encryption Standard . This system was the first to receive the status of a state standard in the field of data encryption. It was developed by IBM specialists and entered into force in the USA in 1977. Algorithm DES has been widely used in storing and transferring data between different computing systems; in postal systems, in electronic drawing systems and in the electronic exchange of commercial information. Standard DES was implemented both in software and in hardware. Enterprises from different countries have launched a mass production of digital devices using DES for data encryption. All devices passed mandatory certification for compliance with the standard.

intuit.ru/2010/edi”> Despite the fact that for some time this system has not had the status of a state standard, it is still widely used and deserves attention when studying block ciphers with a private key.

Key length in algorithm DES is 56 bits. It is with this fact that the main controversy regarding the ability of DES to withstand various attacks is connected. As you know, any block cipher with a private key can be cracked by trying all possible combinations of keys. With a key length of 56 bits, 2 ⁵⁶ different keys are possible. If a computer enumerates 1,000,000 keys in one second (which is approximately equal to 2 ²⁰ ), then enumeration of all 2 ⁵⁶ keys will require 2 ³⁶ seconds or just over two thousand years, which, of course, is unacceptable for attackers.

However, more expensive and faster computing systems than a personal computer are possible. For example, if it is possible to combine a million processors for parallel computing, then the maximum key selection time is reduced to approximately 18 hours. This time is not too long, and a cryptanalyst, equipped with such expensive equipment, may well perform an opening of data encrypted ^DES for a reasonable time.

At the same time, it can be noted that the DES system can be used in small and medium-sized applications for encrypting data of little value. For the encryption of data of national importance or of significant commercial value, the system DES should of course not be used at present. In 2001, after a specially announced competition in the United States, a new block cipher standard was adopted, called AES (Advanced Encryption Standard) , which was based on the cipher Rijndael , developed by Belgian specialists. This cipher is discussed at the end of the lecture.

intuit.ru/2010/edi”> Basic parameters DES : block size 64 bits, key length 56 bits, number of rounds – 16. DES is a classic Feishtel network with two branches. The algorithm converts a 64-bit input data block into a 64-bit output block in several rounds. Standard DES is built on the combined use of permutation, substitution and gamma. Encrypted data must be in binary form.

Encryption

The general structure of DES is shown in
rice.
4.1. The process of encryption of each 64-bit block of source data can be divided into three stages:

1. initial preparation of the data block;
2. 16 rounds “main cycle”;
3. final processing of the data block.

The first step is an initial permutation of the 64-bit original block of text, during which the bits are rearranged in a certain way.

At the next (main) stage, the block is divided into two parts (branches) of 32 bits each. The right branch is converted using some function F and the corresponding partial key obtained from the main encryption key using a special key conversion algorithm. Then the data is exchanged between the left and right branches of the block. This is repeated 16 times in a cycle.

Finally, at the third stage, the result obtained after sixteen steps of the main loop is permuted. This permutation is the reverse of the original permutation.

Fig.
4.1.
General scheme DES

Let’s consider in more detail all stages of cryptographic transformation according to the standard DES .

At the first stage, the 64-bit block of source data is subjected to an initial permutation. In the literature, this operation is sometimes called whitening. During the initial permutation, the bits of the data block are reordered in a certain way. This operation imparts some “randomness” to the original message, reducing the possibility of using cryptanalysis by statistical methods.

Simultaneously with the initial permutation of the data block, an initial permutation of 56 bits of the key is performed. From
rice.
4.1. it can be seen that in each of the rounds the corresponding 48-bit partial key K _i is used. Keys K _i are obtained according to a certain algorithm, using each of the bits of the initial key several times. In each round, the 56-bit key is divided into two 28-bit halves. The halves are then shifted to the left by one or two beats, depending on the round number. After the shift, 48 of the 56 bits are selected in a certain way. Since this not only selects a subset of the bits, but also changes their order, this operation is called a “swap-swap” operation. Its result is a set of 48 bits. On average, each bit of the original 56-bit key is used in 14 of the 16 subkeys, although not all bits are used the same number of times.

Next, the main transformation cycle is performed, organized by the Feishtel network and consisting of 16 identical rounds. However, in each round
rice.
4.2) an intermediate 64-bit value is obtained, which is then processed in the next round.

Fig.
4.2.
Structure of one DES round

The left and right branches of each intermediate value are treated as separate 32-bit values, denoted L and R.

First, the right side of block R _i is expanded to 48 bits using a table that defines a permutation plus an extension of 16 bits. This operation adjusts the size of the right half to match the size of the key to perform the XOR operation. In addition, due to the execution of this operation, the dependence of all bits of the result on the bits of the original data and the key increases faster (this is called the “avalanche effect”). The stronger the avalanche effect when using one or another encryption algorithm, the better.

After permuting with expansion, the resulting 48-bit value is XORed with the 48-bit subkey K _i . Then the resulting 48-bit value is fed to the input of the substitution block S (from English Substitution – substitution), the result of which is a 32-bit value. Substitution is performed in eight substitution boxes or eight S-boxes. When this operation is performed, 48 data bits are divided into eight 6-bit sub-blocks, each of which is replaced by four bits in its substitution table. Substitution using S-boxes is one of the most important steps DES . The substitution tables for this operation are specially designed by experts to ensure maximum safety. The result of this step is eight 4-bit blocks, which are again combined into a single 32-bit value.

Next, the resulting 32-bit value is processed using a permutation P (from the English. Permutation – permutation), which does not depend on the key used. The goal of the permutation is to reorder the bits as much as possible so that in the next round of encryption, each bit is likely to be handled by a different S-box.

Finally, the result of the permutation is XORed with the left half of the original 64-bit data block. Then the left and right halves are reversed and the next round begins.

After sixteen rounds of encryption, a final permutation of the result is performed. This permutation is inverse (reverse) to the initial permutation.

After completing all the above steps, the data block is considered fully encrypted and you can proceed to encrypt the next block of the original message.

If you carefully read the description of DES , you will see that the developers have made every effort to make the process of opening encrypted messages as difficult as possible. Even a simple description of DES on paper looks quite complicated, let alone its software implementation! To develop a correctly and optimally functioning program completely in accordance with DES , probably, only experienced programmers can do it. Some difficulties arise in software implementation, such as the initial permutation or expansion permutation. These difficulties are related to the fact that it was originally planned to implement DES hardware only. All operations used in the standard are easily performed by hardware units, and there are no difficulties with implementation. However, some time after the publication of the standard, software developers decided not to stand aside and also take up the creation of encryption systems.