DES - Data Encryption Standard

What is DES?

DES stands for Data Encryption Standard. It’s a symmetric-key block cipher used to encrypt and decrypt data. DES was one of the earliest encryption standards adopted for securing sensitive information in government and commercial systems.

Why is DES useful?

• DES was a foundational encryption method that helped shape modern cryptography.

• It was useful because: * Encrypted data to prevent unauthorized access * Enabled secure communication over untrusted networks * Standardized encryption across industries and governments * Although now considered insecure, DES led to stronger algorithms like AES

How it works

• Key generation – 56-bit secret key (plus 8 parity bits = 64 bits total)

• Encryption – Plaintext is split into 64-bit blocks, encrypted using 16 transformation rounds

• Transmission/Storage – Ciphertext is securely sent or stored

• Decryption – Same key is used to reverse the encryption process

Where is DES used?

• Though largely obsolete, DES was used in: * Banking systems – Encrypting ATM PINs and financial data * Smart cards – Early secure authentication methods * Legacy systems – Some still use DES or Triple DES (3DES) * VPNs and secure tunnels – Former use in IPsec and SSL/TLS

Which OSI layer does this protocol belong to?

• DES operates at the Presentation Layer (Layer 6)

• Handles encryption and decryption, affecting how data is formatted for the application

• Ensures confidentiality before the data reaches the application layer

Topics in this section,

• Learnings in this section

• Terminology

• Version Info

• DES Version&RFC Details

• DES Basic Setup on Ubuntu using IPv4

• DES Basic Setup on Ubuntu using IPv6

• DES Protocol Packet Details

• DES Usecases

• DES Basic Features

• DES Feature : Symmetric Key Cipher

• DES Feature : Block Cipher

• DES Feature : Key Size

• DES Feature : Feistel Structure

• DES Feature : Initial & Final Permutations

• DES Feature : Subkeys Generation

• DES Feature : S-Boxes

• DES Feature : Fast in Hardware

• DES Feature : Vulnerable to Brute Force

• DES Feature : Superseded by AES

• Reference links

Learnings in this section

• In this section, you are going to learn

Terminology

• Terminology

Version Info

• Version Info

DES Version&RFC Details

DES Version	DES Number	Year	Core Idea / Contribution
Original DES Standard	FIPS PUB 46	1977	First official symmetric encryption standard by NBS (now NIST), based on IBMs Lucifer cipher.
DES Revision 1	FIPS PUB 46-1	1988	Reaffirmed DES with no technical changes.
DES Revision 2	FIPS PUB 46-2	1993	Reaffirmed DES again; introduced Triple DES (3DES) as an option.
DES Final Revision	FIPS PUB 46-3	1999	Officially included Triple DES (TDEA); recommended stronger alternatives.
DES in IPsec	RFC 2405	1998	Specifies use of DES-CBC in IPsec ESP protocol.
DES in IP Security	RFC 1829	1995	Defines DES-CBC for securing IP traffic.
DES Security Advisory	RFC 4772	2006	Discusses vulnerabilities of DES and recommends migration to AES 1.
DES Withdrawal	FIPS PUB 46-3 (Withdrawn)	2005	DES officially withdrawn due to weak key size; AES adopted as replacement.

DES Basic Setup on Ubuntu using IPv4

• Setup

DES Basic Setup on Ubuntu using IPv6

• Setup

DES Protocol Packet Details

DES Encryption Packet

S.No	Protocol Packets	Description	Size(Bytes)
1	DES Encryption Packet	Used to encrypt a 64-bit block of plaintext using a 56-bit symmetric key.	128
	Plaintext Block	The original data to be encrypted.	8
	Key	56-bit key + 8 parity bits (total 64 bits).	8
	Initial Permutation (IP)	Rearranges the bits of the plaintext before processing.	8 (reordered)
	Round Keys	16 subkeys generated from the main key, one for each round.	6 16 = 96
	Feistel Rounds	16 rounds of processing using expansion, substitution, permutation, and XOR.	Internal
	Final Permutation (FP)	Inverse of the initial permutation applied at the end.	8 (reordered)
	Ciphertext Block	The encrypted output after all rounds.	8

DES Decryption Packet

S.No	Protocol Packets	Description	Size(Bytes)
2	DES Decryption Packet	Used to decrypt a 64-bit ciphertext block using the same symmetric key.	128
	Ciphertext Block	The encrypted data to be decrypted.	8
	Key	Same 56-bit key used during encryption.	8
	Initial Permutation (IP)	Rearranges the bits of the ciphertext before processing.	8 (reordered)
	Round Keys (Reversed)	Same 16 subkeys used in reverse order.	96
	Feistel Rounds	16 rounds of inverse processing.	Internal
	Final Permutation (FP)	Inverse of the initial permutation applied at the end.	8 (reordered)
	Plaintext Block	The original data recovered after decryption.	8

DES Usecases

S.no	Use Case	Description
1	Banking & Financial Systems	Used to encrypt ATM PINs, transactions, and interbank communications.
2	Smart Cards	Early smart cards used DES for secure authentication and data protection.
3	Secure Email	DES was used in early secure email systems for encrypting message content.
4	File & Disk Encryption	Used in legacy systems to encrypt files and hard drives.
5	Telecommunications	Employed in securing voice and data transmissions over networks.
6	VPNs and IPsec	DES-CBC was used in early IPsec implementations for encrypting IP packets.
7	Government Systems	Adopted by U.S. federal agencies before AES for protecting sensitive data.
8	Legacy Embedded Systems	Still found in older embedded systems where updates are limited.
9	Triple DES (3DES) Systems	DES used in a chained form (3DES) to extend security in older systems.
10	Digital Payment Systems	Used in early EMV card standards and POS terminals for transaction security.

DES Basic Features

S.no	Feature	Description
1	Symmetric Key Cipher	Uses the same key for both encryption and decryption.
2	Block Cipher	Operates on fixed-size blocks of 64 bits (8 bytes).
3	Key Size	Uses a 56-bit key (plus 8 parity bits, making 64 bits total).
4	Feistel Structure	Based on a 16-round Feistel network for encryption and decryption.
5	Initial & Final Permutations	Applies bit-level permutations at the start and end of processing.
6	Subkeys Generation	Generates 16 round keys from the main key using key scheduling.
7	S-Boxes	Uses 8 substitution boxes (S-boxes) for non-linear transformation.
8	Fast in Hardware	Originally optimized for hardware implementation (e.g., chip-based encryption).
9	Vulnerable to Brute Force	56-bit key is now considered too short for modern security needs.
10	Superseded by AES	DES is now deprecated and replaced by AES for stronger encryption.

DES Feature : Symmetric Key Cipher

Symmetric Key Cipher - Testcases

Symmetric Key Cipher
#	Test Case	Description	Expected Result
1	Encrypt with DES	Use 56-bit key	Ciphertext generated
2	Decrypt with DES	Use same 56-bit key	Plaintext recovered
3	Encrypt and Decrypt with Same Key	Symmetric operation	Data integrity maintained
4	Encrypt and Decrypt with Different Keys	Use wrong key for decryption	Decryption fails or garbage
5	Encrypt Empty String	Encrypt “”	Valid ciphertext generated
6	Decrypt Empty Ciphertext	Decrypt “”	Empty string returned
7	Encrypt Short Text	Encrypt “Hi”	Ciphertext generated
8	Encrypt Long Text	Encrypt large input	Ciphertext generated
9	Encrypt Binary Data	Encrypt byte stream	Ciphertext generated
10	Decrypt Binary Ciphertext	Decrypt byte stream	Original data recovered
11	Use Hex Key	Use hexadecimal key	Encryption succeeds
12	Use Base64 Key	Use base64-encoded key	Encryption succeeds
13	Use Random Key	Generate random 56-bit key	Encryption and decryption succeed
14	Use Static Key	Use fixed key	Consistent results
15	Use Weak Key	Use known weak DES key	Encryption works but insecure
16	Use Semi-Weak Key	Use semi-weak DES key pair	Encryption works but insecure
17	Use Strong Key	Use high-entropy key	Secure encryption
18	Use Invalid Key Length	Use 40-bit key	Error or rejection
19	Use Key Padding	Pad key to 56 bits	Encryption succeeds
20	Encrypt with ECB Mode	Use DES in ECB	Ciphertext generated
21	Encrypt with CBC Mode	Use DES in CBC	Ciphertext generated
22	Encrypt with CFB Mode	Use DES in CFB	Ciphertext generated
23	Encrypt with OFB Mode	Use DES in OFB	Ciphertext generated
24	Encrypt with CTR Mode	Use DES in CTR	Ciphertext generated
25	Encrypt with IV	Use initialization vector	Encryption succeeds
26	Reuse IV	Use same IV in CBC	Insecure encryption
27	Use Different IVs	Encrypt same plaintext	Different ciphertexts
28	Encrypt with Padding	Use PKCS#5 padding	Ciphertext generated
29	Decrypt with Padding	Remove padding	Plaintext recovered
30	Encrypt Without Padding	Input is block-aligned	Ciphertext generated
31	Encrypt Non-Aligned Data	Add padding	Ciphertext generated
32	Encrypt with Hardware Support	Use DES hardware	Fast encryption
33	Encrypt with Software Library	Use OpenSSL or PyCryptodome	Encryption succeeds
34	Encrypt with Custom Implementation	Use own DES code	Works if correct
35	Encrypt with Key Rotation	Change keys periodically	Encryption remains secure
36	Encrypt with Key Expiry	Use expired key	Encryption fails or flagged
37	Encrypt with KMS	Retrieve key from key management system	Encryption succeeds
38	Encrypt with Secure Element	Use secure chip	Encryption succeeds
39	Encrypt with TPM	Use Trusted Platform Module	Encryption succeeds
40	Encrypt with HSM	Use Hardware Security Module	Encryption succeeds
41	Encrypt with Logging	Log key usage	Logs generated
42	Encrypt with SIEM	Send logs to SIEM	Events visible
43	Encrypt with Access Control	Restrict key usage	Unauthorized blocked
44	Encrypt with Key Backup	Use backup key	Encryption continues
45	Encrypt with Key Revocation	Revoke compromised key	Key no longer usable
46	Encrypt with Key Derivation	Derive key from password	Encryption succeeds
47	Encrypt with Compliance Policy	Follow DES usage policy	Policy enforced
48	Encrypt with Legacy System	Use DES for compatibility	Encryption succeeds
49	Encrypt with Triple DES	Use 3DES for stronger security	Ciphertext generated
50	Encrypt with DES in Hybrid System	Combine with RSA	Symmetric key encrypted securely

DES Feature : Block Cipher

Block Cipher - Testcases

#	Test Case	Description	Expected Result
1	Encrypt 64-bit block	Encrypt exactly 8 bytes	One ciphertext block generated
2	Encrypt 128-bit block	Encrypt 16 bytes	Two ciphertext blocks generated
3	Encrypt 32-bit block	Encrypt 4 bytes	Padding applied
4	Encrypt 65-bit block	Encrypt slightly over 8 bytes	Two ciphertext blocks generated
5	Encrypt 0-bit block	Encrypt empty input	Empty ciphertext
6	Encrypt 512-bit block	Encrypt 64 bytes	8 ciphertext blocks generated
7	Encrypt with PKCS#5 padding	Pad to 64-bit block size	Valid ciphertext
8	Encrypt with ISO/IEC 7816-4 padding	Use alternate padding	Valid ciphertext
9	Encrypt with no padding	Input is multiple of 8 bytes	Ciphertext generated
10	Encrypt with incorrect padding	Input not padded correctly	Error or incorrect decryption
11	Decrypt 64-bit block	Decrypt one block	Original plaintext recovered
12	Decrypt 128-bit block	Decrypt two blocks	Original plaintext recovered
13	Decrypt with wrong padding	Padding mismatch	Error or garbage output
14	Encrypt with ECB mode	Block-by-block encryption	Identical blocks same ciphertext
15	Encrypt with CBC mode	Chained block encryption	Ciphertext varies with IV
16	Encrypt with CFB mode	Stream-like block encryption	Ciphertext generated
17	Encrypt with OFB mode	Output feedback mode	Ciphertext generated
18	Encrypt with CTR mode	Counter mode	Ciphertext generated
19	Encrypt with same plaintext blocks	ECB mode	Identical ciphertext blocks
20	Encrypt with different IVs	CBC mode	Different ciphertexts
21	Encrypt with reused IV	CBC mode	Ciphertext same, insecure
22	Encrypt with IV = 0	CBC mode	Ciphertext generated, insecure
23	Encrypt with random IV	CBC mode	Ciphertext varies
24	Encrypt with invalid IV size	IV 64 bits	Error or rejection
25	Encrypt with valid IV size	IV = 64 bits	Encryption succeeds
26	Encrypt with block-aligned data	No padding needed	Ciphertext generated
27	Encrypt with non-aligned data	Padding applied	Ciphertext generated
28	Encrypt with UTF-8 text	Multibyte characters	Ciphertext generated
29	Encrypt with ASCII text	Single-byte characters	Ciphertext generated
30	Encrypt with binary data	Raw bytes	Ciphertext generated
31	Encrypt with JSON data	Structured text	Ciphertext generated
32	Encrypt with XML data	Structured text	Ciphertext generated
33	Encrypt with image data	Binary file	Ciphertext generated
34	Encrypt with audio data	Binary file	Ciphertext generated
35	Encrypt with video data	Large binary file	Ciphertext generated
36	Encrypt with compressed data	ZIP or GZIP	Ciphertext generated
37	Encrypt with encrypted input	Double encryption	Ciphertext generated
38	Encrypt with corrupted block	Modify one block	Decryption fails or partial recovery
39	Encrypt with tampered IV	Modify IV	Decryption fails or incorrect
40	Encrypt with block chaining	CBC mode	Each block depends on previous
41	Encrypt with block independence	ECB mode	Each block independent
42	Encrypt with block size 64 bits	Invalid block size	Error or rejection
43	Encrypt with 64-bit aligned file	No padding needed	Ciphertext generated
44	Encrypt with 1MB file	Multiple blocks	Ciphertext generated
45	Encrypt with 1GB file	Large input	Ciphertext generated
46	Encrypt with streaming input	Block-by-block processing	Ciphertext generated
47	Encrypt with block corruption	Flip bits in ciphertext	Decryption fails
48	Encrypt with block replay	Replay old ciphertext block	Potential vulnerability
49	Encrypt with block reordering	Change block order	Decryption fails or incorrect
50	Encrypt with block visualization	Show block-by-block transformation	64-bit blocks shown

DES Feature : Key Size

Key size - Testcases

#	Test Case	Description	Expected Result
1	Use 56-bit key	Standard DES key	Encryption succeeds
2	Use 64-bit key with parity	Full DES key format	Encryption succeeds
3	Use key with incorrect length	Use 40-bit key	Error or rejection
4	Use key with extra bits	Use 80-bit key	Error or rejection
5	Use all-zero key	Weak key	Encryption works but insecure
6	Use all-one key	Weak key	Encryption works but insecure
7	Use alternating bits key	Patterned key	Encryption works
8	Use random 56-bit key	High entropy key	Secure encryption
9	Use base64-encoded key	Decode and use	Encryption succeeds
10	Use hex-encoded key	Convert and use	Encryption succeeds
11	Use key with parity bits	Validate parity	Encryption succeeds
12	Use key without parity bits	Skip parity check	Encryption may fail
13	Use weak DES key	Known weak key	Encryption works but insecure
14	Use semi-weak DES key	Known semi-weak pair	Encryption works but insecure
15	Use strong DES key	High entropy, no patterns	Secure encryption
16	Use key with parity error	Invalid parity bits	Key rejected
17	Use key with correct parity	Valid parity bits	Key accepted
18	Use key with parity check disabled	Skip parity validation	Encryption succeeds
19	Use key with parity check enabled	Validate parity bits	Encryption succeeds
20	Use key from password	Derive 56-bit key	Encryption succeeds
21	Use key from passphrase	Use hash or KDF	Encryption succeeds
22	Use key from KMS	Retrieve key securely	Encryption succeeds
23	Use key from HSM	Use hardware key	Encryption succeeds
24	Use key from TPM	Trusted Platform Module	Encryption succeeds
25	Use key from secure element	Embedded chip	Encryption succeeds
26	Use key from environment variable	Load key dynamically	Encryption succeeds
27	Use key from config file	Load key from file	Encryption succeeds
28	Use key from user input	Enter key manually	Encryption succeeds
29	Use key rotation	Change key periodically	Encryption remains secure
30	Use key expiration	Expire old key	Encryption fails or flagged
31	Use key revocation	Revoke compromised key	Key no longer usable
32	Use key backup	Use backup key	Encryption continues
33	Use key with access control	Restrict usage	Unauthorized blocked
34	Use key with audit logging	Log key usage	Logs generated
35	Use key with SIEM integration	Monitor key events	Events visible
36	Use key with compliance policy	Enforce key standards	Policy enforced
37	Use key with encryption policy	Match key size requirement	Encryption succeeds
38	Use key with legacy system	DES compatibility	Encryption succeeds
39	Use key with Triple DES	Extend key for 3DES	Stronger encryption
40	Use key with hybrid encryption	Combine with RSA	Symmetric key encrypted
41	Use key with padding	Pad to 64 bits	Encryption succeeds
42	Use key with bit masking	Mask to 56 bits	Encryption succeeds
43	Use key with bit shifting	Adjust key bits	Encryption succeeds
44	Use key with entropy check	Validate randomness	Secure key
45	Use key with checksum	Validate integrity	Key accepted
46	Use key with fingerprint	Identify key	Key verified
47	Use key with hash	Store securely	Key verified
48	Use key with encryption	Encrypt key itself	Secure key storage
49	Use key with secure transmission	Send over TLS	Key protected
50	Use key with secure storage	Store in encrypted vault	Key protected

DES Feature : Feistel Structure

Feistel Structure - Testcases

#	Test Case	Description	Expected Result
1	Execute 16 Feistel rounds	Standard DES encryption	Ciphertext generated
2	Reverse 16 Feistel rounds	Standard DES decryption	Plaintext recovered
3	Encrypt with 1 round	Single Feistel round	Incomplete encryption
4	Encrypt with 8 rounds	Half of DES rounds	Weaker encryption
5	Encrypt with 16 rounds	Full DES encryption	Secure ciphertext
6	Decrypt with 16 rounds	Full DES decryption	Original plaintext
7	Swap halves after final round	Final Feistel step	Correct ciphertext
8	Skip final swap	Omit last step	Incorrect result
9	Use same round function	Reuse F-function	Encryption succeeds
10	Use different round functions	Vary F-function	Encryption still valid
11	Use incorrect round order	Shuffle rounds	Decryption fails
12	Use correct round order	Maintain sequence	Decryption succeeds
13	Use same key for all rounds	Static key	Works but insecure
14	Use different keys per round	Key schedule applied	Secure encryption
15	Use reversed key schedule	Decrypt ciphertext	Plaintext recovered
16	Modify one round	Tamper with round logic	Decryption fails
17	Skip one round	Incomplete Feistel network	Decryption fails
18	Duplicate a round	Repeat one round	Decryption fails
19	Log each round	Output intermediate states	16 rounds logged
20	Visualize round structure	Show L and R halves	Feistel flow confirmed
21	Encrypt with faulty F-function	Use incorrect logic	Decryption fails
22	Encrypt with correct F-function	Use standard logic	Encryption succeeds
23	Analyze round diffusion	Track bit spread	High diffusion
24	Analyze round confusion	Track substitution	High confusion
25	Test avalanche effect	Flip 1 input bit	Major output change
26	Test key sensitivity	Flip 1 key bit	Major output change
27	Encrypt with round key reuse	Use same key twice	Works but insecure
28	Encrypt with round key rotation	Rotate keys	Encryption succeeds
29	Encrypt with round key derivation	Use key schedule	Keys generated correctly
30	Encrypt with round key corruption	Modify one key	Decryption fails
31	Encrypt with round input corruption	Modify L or R	Decryption fails
32	Encrypt with round output corruption	Modify output	Decryption fails
33	Encrypt with round logging	Log L, R, and F	Debug info available
34	Encrypt with round masking	Mask intermediate values	Still works
35	Encrypt with round timing	Measure time per round	Consistent timing
36	Encrypt with round profiling	Analyze performance	Round-by-round stats
37	Encrypt with round visualization	Show Feistel flow	16 rounds shown
38	Encrypt with round animation	Animate L/R swaps	Visual confirmation
39	Encrypt with round checksum	Validate round output	Integrity confirmed
40	Encrypt with round hash	Hash each round output	Debugging aid
41	Encrypt with round parity check	Check bit parity	Validated
42	Encrypt with round fault injection	Flip bit in round	Output corrupted
43	Encrypt with round reordering	Change round sequence	Decryption fails
44	Encrypt with round skipping	Skip round 8	Decryption fails
45	Encrypt with round duplication	Repeat round 5	Decryption fails
46	Encrypt with round inversion	Invert round logic	Decryption fails
47	Encrypt with round tracing	Trace L and R	Debugging aid
48	Encrypt with round comparison	Compare with reference	Output matches
49	Encrypt with round validation	Validate each round	All rounds pass
50	Encrypt with round simulation	Simulate Feistel network	Correct ciphertext

DES Feature : Initial & Final Permutations

Initial & Final Permutations - Testcases

#	Test Case	Description	Expected Result
1	Apply Initial Permutation (IP)	Permute 64-bit input	Bits rearranged
2	Apply Final Permutation (FP)	Permute 64-bit output	Original bit order restored
3	Skip Initial Permutation	Omit IP step	Incorrect ciphertext
4	Skip Final Permutation	Omit FP step	Incorrect plaintext
5	Apply IP then FP	Apply both in sequence	Original input recovered
6	Apply FP then IP	Reverse order	Incorrect result
7	Apply IP only	No FP	Output not usable
8	Apply FP only	No IP	Output not usable
9	Validate IP table	Check against DES spec	Matches standard
10	Validate FP table	Check against DES spec	Matches standard
11	Invert IP	Apply FP to IP output	Original input recovered
12	Invert FP	Apply IP to FP output	Original input recovered
13	Modify IP table	Change permutation	Decryption fails
14	Modify FP table	Change permutation	Decryption fails
15	Use random permutation	Replace IP/FP	Decryption fails
16	Use identity permutation	No change in bit order	Decryption fails
17	Log IP output	Show permuted bits	Matches expected
18	Log FP output	Show final permutation	Matches expected
19	Visualize IP	Show bit positions before/after	Bit mapping confirmed
20	Visualize FP	Show bit positions before/after	Bit mapping confirmed
21	Encrypt with IP/FP	Standard DES	Correct ciphertext
22	Decrypt with IP/FP	Standard DES	Correct plaintext
23	Encrypt without IP	Skip IP	Decryption fails
24	Decrypt without FP	Skip FP	Decryption fails
25	Encrypt with swapped IP/FP	Reverse roles	Decryption fails
26	Encrypt with partial IP	Apply only half	Decryption fails
27	Encrypt with partial FP	Apply only half	Decryption fails
28	Encrypt with IP logging	Log each bit move	Debug info available
29	Encrypt with FP logging	Log each bit move	Debug info available
30	Encrypt with IP visualization	Show bit flow	Educational output
31	Encrypt with FP visualization	Show bit flow	Educational output
32	Encrypt with IP masking	Mask bits during IP	Decryption fails
33	Encrypt with FP masking	Mask bits during FP	Decryption fails
34	Encrypt with IP fault injection	Flip bit in IP	Output corrupted
35	Encrypt with FP fault injection	Flip bit in FP	Output corrupted
36	Encrypt with IP timing	Measure time	Minimal overhead
37	Encrypt with FP timing	Measure time	Minimal overhead
38	Encrypt with IP profiling	Analyze performance	Fast operation
39	Encrypt with FP profiling	Analyze performance	Fast operation
40	Encrypt with IP validation	Compare to reference	Matches expected
41	Encrypt with FP validation	Compare to reference	Matches expected
42	Encrypt with IP test vector	Use known input	Output matches
43	Encrypt with FP test vector	Use known output	Input recovered
44	Encrypt with IP/FP disabled	Bypass both	Incompatible with standard DES
45	Encrypt with IP/FP enabled	Use both	Standard DES behavior
46	Encrypt with IP/FP in hardware	Use hardware DES	Fast and correct
47	Encrypt with IP/FP in software	Use software DES	Correct result
48	Encrypt with IP/FP in simulation	Simulate bit flow	Matches DES spec
49	Encrypt with IP/FP in test harness	Unit test IP/FP	Passes all checks
50	Encrypt with IP/FP in educational tool	Teach DES structure	Accurate visualization

DES Feature : Subkeys Generation

Subkeys Generation - Testcases

#	Test Case	Description	Expected Result
1	Generate 16 subkeys	From 56-bit key	16 round keys generated
2	Validate subkey length	Each subkey	48 bits
3	Use correct PC-1 table	Initial key permutation	56-bit key derived
4	Use correct PC-2 table	Subkey permutation	48-bit subkeys derived
5	Apply left shifts	Shift key halves	Correct rotation per round
6	Use standard shift schedule	Follow DES spec	Valid subkeys
7	Use custom shift schedule	Modify shifts	Subkeys differ
8	Use all-zero key	Generate subkeys	Subkeys generated (insecure)
9	Use all-one key	Generate subkeys	Subkeys generated (insecure)
10	Use alternating bits key	Generate subkeys	Subkeys generated
11	Use random key	Generate subkeys	Unique subkeys
12	Use weak key	Known weak key	Repeating subkeys
13	Use semi-weak key	Known semi-weak pair	Subkeys repeat in pattern
14	Use strong key	High entropy	Secure subkeys
15	Log subkeys	Output all 16 subkeys	Debug info available
16	Visualize subkey generation	Show bit flow	Educational output
17	Compare subkeys	Ensure uniqueness	All subkeys differ
18	Compare subkeys with reversed key	Use reversed input key	Different subkeys
19	Use incorrect PC-1 table	Wrong permutation	Invalid subkeys
20	Use incorrect PC-2 table	Wrong permutation	Invalid subkeys
21	Skip left shifts	No rotation	Subkeys incorrect
22	Apply double shifts	Shift too far	Subkeys incorrect
23	Use only 1 subkey	Encrypt with 1 round	Incomplete encryption
24	Use 8 subkeys	Encrypt with 8 rounds	Weaker encryption
25	Use 16 subkeys	Full DES encryption	Secure encryption
26	Use reversed subkeys	Decrypt ciphertext	Plaintext recovered
27	Use wrong subkey order	Shuffle subkeys	Decryption fails
28	Use same subkey for all rounds	Static key	Works but insecure
29	Use different keys per round	Proper key schedule	Secure encryption
30	Use subkeys in ECB mode	Block encryption	Works as expected
31	Use subkeys in CBC mode	Chained encryption	Works as expected
32	Use subkeys in CFB mode	Stream-like encryption	Works as expected
33	Use subkeys in OFB mode	Output feedback	Works as expected
34	Use subkeys in CTR mode	Counter mode	Works as expected
35	Encrypt with corrupted subkey	Modify one subkey	Decryption fails
36	Encrypt with missing subkey	Skip one round	Decryption fails
37	Encrypt with extra subkey	Add 17th key	Decryption fails
38	Encrypt with subkey masking	Mask bits	Decryption fails
39	Encrypt with subkey logging	Log each round key	Debug info available
40	Encrypt with subkey profiling	Measure generation time	Fast operation
41	Encrypt with subkey validation	Check bit length	All 48 bits
42	Encrypt with subkey entropy check	Measure randomness	High entropy
43	Encrypt with subkey hash	Hash each subkey	Unique hashes
44	Encrypt with subkey fingerprint	Identify each key	Unique fingerprints
45	Encrypt with subkey visualization	Show key schedule	16 keys displayed
46	Encrypt with subkey simulation	Simulate generation	Matches DES spec
47	Encrypt with subkey test vector	Use known key	Subkeys match reference
48	Encrypt with subkey compliance	FIPS 46-3 check	Compliant
49	Encrypt with subkey in hardware	Use DES chip	Subkeys generated
50	Encrypt with subkey in software	Use DES library	Subkeys generated

DES Feature : S-Boxes

S-Boxes - Testcases

#	Test Case	Description	Expected Result
1	Use all 8 S-boxes	Apply during F-function	Substitution performed
2	Validate S-box input size	6-bit input	Accepted
3	Validate S-box output size	4-bit output	Correct size
4	Use S-box 1	Apply to input	4-bit output generated
5	Use S-box 2	Apply to input	4-bit output generated
6	Use S-box 3	Apply to input	4-bit output generated
7	Use S-box 4	Apply to input	4-bit output generated
8	Use S-box 5	Apply to input	4-bit output generated
9	Use S-box 6	Apply to input	4-bit output generated
10	Use S-box 7	Apply to input	4-bit output generated
11	Use S-box 8	Apply to input	4-bit output generated
12	Apply all S-boxes in F-function	48-bit input 32-bit output	Substitution complete
13	Use invalid S-box index	Index out of range	Error or rejection
14	Use invalid S-box input	>6 bits	Error or rejection
15	Use invalid S-box output	>4 bits	Error or rejection
16	Use custom S-box	Replace standard	Encryption works if reversible
17	Use faulty S-box	Incorrect values	Decryption fails
18	Use identity S-box	No substitution	Weak encryption
19	Use random S-box	Random values	Unpredictable output
20	Use S-box with fixed input	Same input each round	Same output
21	Use S-box with varying input	Different inputs	Different outputs
22	Analyze S-box non-linearity	Check output patterns	High non-linearity
23	Analyze S-box confusion	Input-output correlation	Low correlation
24	Analyze S-box diffusion	Bit change in input multiple output bits	Confirmed
25	Flip 1 input bit	Observe S-box output	Output changes significantly
26	Flip 1 output bit	Trace back to input	Not easily reversible
27	Log S-box input/output	Debugging	Values match spec
28	Visualize S-box mapping	Input output table	Matches DES spec
29	Compare S-boxes	Check uniqueness	All 8 are distinct
30	Use S-box in round 1	Apply during encryption	Output contributes to round result
31	Use S-box in round 16	Apply during final round	Output contributes to ciphertext
32	Use S-box in decryption	Same S-boxes used	Reversible transformation
33	Use S-box with test vector	Known input	Output matches reference
34	Use S-box with all-zero input	6-bit 0	Valid output
35	Use S-box with all-one input	6-bit 1s	Valid output
36	Use S-box with alternating bits	101010	Valid output
37	Use S-box with random input	Random 6-bit	Valid output
38	Use S-box with boundary input	000000 and 111111	Valid outputs
39	Use S-box with middle input	100011	Valid output
40	Use S-box with invalid row/column	Out-of-bounds	Error or fallback
41	Use S-box with parity bits	Ignore parity	Output unaffected
42	Use S-box with masking	Mask input bits	Output changes
43	Use S-box with bitwise operations	Extract row/column	Correct mapping
44	Use S-box with lookup table	Precomputed values	Fast substitution
45	Use S-box with software implementation	Python/C/Java	Output matches spec
46	Use S-box with hardware implementation	FPGA/ASIC	Output matches spec
47	Use S-box with simulation	Simulate substitution	Output verified
48	Use S-box with visualization tool	Show input/output flow	Educational output
49	Use S-box with entropy test	Measure randomness	High entropy
50	Use S-box with compliance check	FIPS 46-3	Matches standard

DES Feature : Fast in Hardware

Fast in Hardware - Testcases

#	Test Case	Description	Expected Result
1	DES on ASIC	Implement DES on custom chip	High-speed encryption
2	DES on FPGA	Implement DES on FPGA board	Fast and flexible
3	DES on smart card	Use chip-based DES	Efficient encryption
4	DES on embedded system	Use microcontroller	Real-time performance
5	DES on hardware security module (HSM)	Use dedicated crypto hardware	High throughput
6	DES on TPM	Use Trusted Platform Module	Secure and fast
7	DES on secure element	Use embedded chip	Fast and secure
8	DES with pipelining	Hardware pipeline stages	Increased throughput
9	DES with parallelism	Parallel block processing	Speedup achieved
10	DES with clock optimization	High-frequency clock	Faster rounds
11	DES with low latency	Measure encryption delay	Minimal latency
12	DES with low power	Measure energy use	Power-efficient
13	DES with minimal gates	Small logic footprint	Hardware-efficient
14	DES with minimal memory	Low RAM/ROM usage	Embedded-friendly
15	DES with hardware key storage	Store key in chip	Secure and fast access
16	DES with hardware IV generation	Generate IV on-chip	Fast initialization
17	DES with hardware RNG	Use chip RNG for keys	Secure key generation
18	DES with hardware padding	Auto-pad input	Fast preprocessing
19	DES with hardware S-boxes	Use lookup tables	Fast substitution
20	DES with hardware shift registers	For key scheduling	Efficient key rotation
21	DES with hardware permutation logic	Implement IP/FP	Fast bit-level ops
22	DES with hardware round logic	16-round pipeline	High-speed processing
23	DES with hardware fault detection	Detect bit flips	Secure operation
24	DES with hardware masking	Prevent side-channel leaks	Secure implementation
25	DES with hardware acceleration	Use crypto co-processor	Speed boost
26	DES with hardware benchmarking	Measure throughput	High performance
27	DES with hardware profiling	Analyze timing	Consistent results
28	DES with hardware simulation	Simulate logic gates	Matches spec
29	DES with hardware synthesis	Convert HDL to chip	Functional design
30	DES with hardware verification	Run test vectors	All pass
31	DES with hardware debugging	Trace signals	Correct logic flow
32	DES with hardware testbench	Simulate input/output	Matches expected
33	DES with hardware timing analysis	Check critical path	Meets timing constraints
34	DES with hardware area analysis	Measure chip area	Compact design
35	DES with hardware power analysis	Measure consumption	Low power
36	DES with hardware latency test	Measure per block	Fast response
37	DES with hardware throughput test	Measure blocks/sec	High throughput
38	DES with hardware integration	Integrate with SoC	Works seamlessly
39	DES with hardware bootloader	Encrypt firmware	Fast secure boot
40	DES with hardware authentication	Use for device ID	Fast verification
41	DES with hardware encryption engine	Dedicated logic	High-speed crypto
42	DES with hardware decryption engine	Dedicated logic	Fast decryption
43	DES with hardware key loader	Load key securely	Fast initialization
44	DES with hardware test mode	Enable diagnostics	Functional validation
45	DES with hardware compliance	FIPS 46-3 check	Meets standard
46	DES with hardware legacy support	Support old systems	Compatible
47	DES with hardware secure boot	Encrypt bootloader	Fast and secure
48	DES with hardware secure storage	Encrypt flash/memory	Fast access
49	DES with hardware crypto library	Use HDL modules	Reusable components
50	DES with hardware co-design	Combine with software	Balanced performance

DES Feature : Vulnerable ro Brute Force

Vulnerable ro Brute Force - Testcases

#	Test Case	Description	Expected Result
1	Brute-force 56-bit key	Try all key combinations	Key found in feasible time
2	Estimate key space	Calculate 2^56	~72 quadrillion keys
3	Brute-force with modern CPU	Use single processor	Key cracked in hours/days
4	Brute-force with GPU	Use parallel processing	Key cracked faster
5	Brute-force with FPGA	Use hardware acceleration	Key cracked in hours
6	Brute-force with ASIC	Use custom chip	Key cracked in minutes
7	Brute-force with cloud	Use distributed computing	Key cracked quickly
8	Brute-force with botnet	Use compromised devices	Key cracked at scale
9	Brute-force with rainbow tables	Precomputed keys	Fast lookup
10	Brute-force with dictionary attack	Try common keys	Key found if weak
11	Brute-force with known plaintext	Use known input/output	Key recovered
12	Brute-force with ciphertext-only	No known plaintext	Still feasible
13	Brute-force with chosen plaintext	Encrypt known values	Key cracked faster
14	Brute-force with chosen ciphertext	Decrypt known values	Key cracked faster
15	Brute-force with partial key	Known key bits	Reduces search space
16	Brute-force with weak key	All-zero key	Easily guessed
17	Brute-force with semi-weak key	Known key pair	Predictable behavior
18	Brute-force with repeated key	Reuse across systems	Key cracked once, reused
19	Brute-force with short key	Use <56-bit key	Even faster attack
20	Brute-force with key reuse	Same key for multiple messages	Easier to crack
21	Brute-force with key pattern	Predictable key structure	Easier to guess
22	Brute-force with entropy analysis	Low entropy key	Easier to crack
23	Brute-force with timing attack	Measure response time	Infer key bits
24	Brute-force with power analysis	Monitor power usage	Infer key bits
25	Brute-force with side-channel attack	Use physical leakage	Key recovered
26	Brute-force with DES test vectors	Known input/output	Key cracked
27	Brute-force with DES in ECB mode	Identical blocks	Easier to analyze
28	Brute-force with DES in CBC mode	IV known	Still vulnerable
29	Brute-force with DES in CFB mode	Stream-like	Still vulnerable
30	Brute-force with DES in OFB mode	Output feedback	Still vulnerable
31	Brute-force with DES in CTR mode	Counter known	Still vulnerable
32	Brute-force with DES in GPG/PGP	Legacy encryption	Key cracked
33	Brute-force with DES in SSL/TLS	Deprecated use	Key cracked
34	Brute-force with DES in Wi-Fi	Legacy WPA	Key cracked
35	Brute-force with DES in banking	Legacy ATM systems	Key cracked
36	Brute-force with DES in smart cards	Legacy cards	Key cracked
37	Brute-force with DES in RFID	Legacy tags	Key cracked
38	Brute-force with DES in satellite	Legacy comms	Key cracked
39	Brute-force with DES in SCADA	Industrial systems	Key cracked
40	Brute-force with DES in IoT	Legacy firmware	Key cracked
41	Brute-force with DES in file encryption	Old archives	Key cracked
42	Brute-force with DES in email	Legacy S/MIME	Key cracked
43	Brute-force with DES in backup	Old encrypted backups	Key cracked
44	Brute-force with DES in DRM	Legacy content	Key cracked
45	Brute-force with DES in password manager	Old vaults	Key cracked
46	Brute-force with DES in database	Legacy encryption	Key cracked
47	Brute-force with DES in firmware	Embedded systems	Key cracked
48	Brute-force with DES in legacy OS	Old operating systems	Key cracked
49	Brute-force with DES in compliance audit	Security review	Flagged as insecure
50	Brute-force with DES in penetration test	Ethical hacking	Key recovered quickly

DES Feature : Superseded by AES

Superseded by AES - Testcases

#	Test Case	Description	Expected Result
1	Use DES in new system	Attempt to implement DES	Rejected by policy
2	Use AES in new system	Implement AES instead	Accepted and secure
3	Compare DES and AES key sizes	56-bit vs 128/192/256-bit	AES is stronger
4	Compare DES and AES block sizes	64-bit vs 128-bit	AES is more secure
5	Compare DES and AES rounds	16 vs 10/12/14	AES is more flexible
6	Attempt FIPS compliance with DES	Use DES	Not compliant
7	Attempt FIPS compliance with AES	Use AES	Compliant
8	Use DES in TLS	Legacy protocol	Deprecated
9	Use AES in TLS	Modern protocol	Secure and accepted
10	Use DES in VPN	Legacy encryption	Not recommended
11	Use AES in VPN	Modern encryption	Secure
12	Use DES in Wi-Fi	WPA1 or WEP	Insecure
13	Use AES in Wi-Fi	WPA2/WPA3	Secure
14	Use DES in file encryption	Legacy archives	Weak protection
15	Use AES in file encryption	Modern tools	Strong protection
16	Use DES in database encryption	Legacy systems	Vulnerable
17	Use AES in database encryption	Modern systems	Secure
18	Use DES in cloud storage	Legacy compatibility	Not secure
19	Use AES in cloud storage	Industry standard	Secure
20	Use DES in mobile apps	Legacy SDKs	Deprecated
21	Use AES in mobile apps	Secure SDKs	Recommended
22	Use DES in smart cards	Legacy cards	Weak encryption
23	Use AES in smart cards	Modern cards	Strong encryption
24	Use DES in government systems	Legacy systems	Deprecated
25	Use AES in government systems	Mandated by NIST	Secure
26	Use DES in banking	Legacy ATMs	Vulnerable
27	Use AES in banking	Secure transactions	Industry standard
28	Use DES in healthcare	Legacy systems	Not HIPAA-compliant
29	Use AES in healthcare	Secure patient data	HIPAA-compliant
30	Use DES in IoT	Legacy firmware	Insecure
31	Use AES in IoT	Lightweight AES	Secure
32	Use DES in firmware	Legacy devices	Vulnerable
33	Use AES in firmware	Secure boot	Recommended
34	Use DES in password managers	Legacy vaults	Weak encryption
35	Use AES in password managers	Modern vaults	Strong encryption
36	Use DES in messaging apps	Legacy protocols	Insecure
37	Use AES in messaging apps	End-to-end encryption	Secure
38	Use DES in compliance audit	Security review	Flagged as insecure
39	Use AES in compliance audit	Security review	Approved
40	Use DES in penetration test	Ethical hacking	Easily cracked
41	Use AES in penetration test	Ethical hacking	Secure
42	Use DES in cryptanalysis test	Brute-force attack	Key recovered
43	Use AES in cryptanalysis test	Brute-force attack	Infeasible
44	Use DES in academic curriculum	Teach legacy crypto	For historical context
45	Use AES in academic curriculum	Teach modern crypto	For practical use
46	Use DES in open-source project	Legacy compatibility	Not recommended
47	Use AES in open-source project	Secure by default	Recommended
48	Use DES in secure email	Legacy S/MIME	Deprecated
49	Use AES in secure email	Modern encryption	Secure
50	Use DES in new cryptographic standard	Attempt inclusion	Rejected in favor of AES

Reference links

• Reference links