What is SHA 2?
Cryptographic hash functions must be understood before learning SHA-2. These algorithms convert any size input into a fixed-length hash. They have a number of important characteristics that qualify them for security applications:
Deterministic: The result of a fixed-length hash will always be exactly the same as the input.
Designed so that slight changes significantly alter the output: Intended to drastically vary the output from even little changes in the input; even a small change in the input will produce a hash that appears to be entirely unrelated.
Fast to calculate: It takes very little time to create a hash from an input.
One-way functions: It is thought to be almost difficult to determine an input based just on its hash with the methods and tools available today. This characteristic is essential to a large portion of global internet security.
Collision-resistant: The same hash cannot be produced by two separate inputs. A “collision” happens when different inputs produce the same hash value. Collisions provide a significant security risk because they can compromise authentication systems, for instance, by enabling an attacker to use a genuine digital signature on a phoney document to falsely identify oneself.
The SHA-2 Family
Instead of being a single algorithm, SHA-2 is a family of six distinct hash functions:
- SHA-224
- SHA-256
- SHA-384
- SHA-512
- SHA-512/224
- SHA-512/256
Despite differences in the hash lengths of their output, these methods have the same fundamental structure. SHA-256 is the most used version.
Variations within the SHA-2 Family
The variations between the SHA-2 algorithms are related to the number of processing rounds, constants, word lengths, block sizes, and hash lengths:
Hash Length: The techniques yield 256, 384, 512, and 224-bit hashes. Higher hash lengths increase collision resistance since it’s harder to find two inputs with the same hash. However, computing bigger hashes takes longer and uses more electricity.
Block Size: Four remaining SHA-2 algorithms SHA-384, SHA-512, SHA-512/224, and SHA-512/256 use 1,024-bit block sizes, while SHA-224 and SHA-256 use 512 bits. For a given input, smaller blocks may require more blocks, but they may calculate faster.
Length of Words, Initialization Variables, and Constants: Initialization variables and constants are 32 bits, while SHA-224 and SHA-256 process input messages in 32-bit words (512-bit block sizes). SHA-2 algorithms employ 64-bit (1,024-bit) blocks. This design option affects hardware compatibility and processing performance, preferably matching CPU register size.
Number of Rounds: While SHA-384, SHA-512, SHA-512/224, and SHA-512/256 need 80 rounds per data block, SHA-224 and SHA-256 utilize 64. The input data, constants, and initialization/working variables are carefully mixed in each round. It becomes progressively more difficult to determine the original input from the hash or to identify an input that generates the same hash as the number of rounds an algorithm completes because the data is more completely mixed.
Truncation: The 512-bit hash in SHA-512/224 and SHA-512/256 is truncated to 256 and 224 bits, respectively. The truncation’s main benefit is length extension resistance. An attacker can recreate a digital signature without knowing the secret value if they know the hashing algorithm, the victim’s data input, and the hash. Trunk hashes lack enough information for various attacks.
Applications of SHA-2
The SHA-2 algorithm family finds widespread usage in a wide range of security applications and protocols:
Security Protocols: Pretty Good Privacy (PGP) and Secure/Multipurpose Internet Mail Extensions (S/MIME) for email encryption, Internet Protocol Security (IPSec, frequently found in VPNs), Transport Layer Security (TLS, found in https websites), and Secure Shell (SSH) for file transfers and remote computer access are all essential components of these security measures.
Data Authentication: From validating evidence to confirming the authenticity of software, SHA-2 hash algorithms are employed to demonstrate that data has not been changed.
Password Hashing: Although it is occasionally employed, for increased security it is usually recommended to utilize programs like bcrypt that are especially made for hashing passwords.
Blockchain Technologies: SHA-256 is essential to Bitcoin’s and other cryptocurrencies’ proof of work mechanism.
US Government Data: Since 2015, all government agencies have been advised to employ algorithms from the SHA-2 or SHA-3 family by the US National Institute of Standards and Technologies (NIST).
History and Transition from SHA-1
With its predecessors, the path to SHA-2 started:
SHA-0: 1993 saw NIST publish it (FIPS 180).
SHA-1: Released as a SHA-0 update in 1995 (FIPS 180-1) following the discovery of flaws. SHA-1 generates a hash of 160 bits. The 160-bit hash length of SHA-1 became a security issue as technology developed, and government organizations were able to launch realistic risks against it. NIST said that it will phase down SHA-1 clearance by 2010 as a result of this.
The update to SHA-2 was necessary after Heartbleed compromised over half a million SSL certificates. Microsoft discontinued SHA-1 support on January 1, 2016, and Windows devices ceased trusting SHA-1 certificates on January 1, 2017. SHA-2 was inescapable and a major worry for web managers.
SHA-2 Algorithm’s Design
The complex architecture of the SHA-2 algorithms guarantees their security features:
One-way Compression Functions: Fundamentally, one-way compression functions are used to build SHA-2 algorithms. A hash or an intermediate hash from a previous block is the only fixed-length output that these functions can generate given two fixed-length inputs (a block of message data and a set of initialization variables) or an intermediate hash.
Davies-Meyer Compression Function: In particular, the Davies-Meyer compression function is used by SHA-2. Adding the initialization variables (or intermediate hash) in modules to the internal processing output (called ‘E’) is one of its distinguishing features. Comparing this structure to other options, it offers advantages in terms of efficiency and simplicity.
Merkle-Damgard Construction: SHA-2 uses the Merkle-Damgard design to structure its one-way compression operations. The hash function’s collision resistance is the goal of this design. In order to do this, it processes input data of any length in fixed-size blocks, padding the last block as needed. Merkle-Damgard strengthening, or length padding, is a crucial component of this design in which the length of the original message is attached to the last padded block.
This strengthening aids in the mathematical demonstration that if the underlying compression function of the hash function is collision-resistant, then the hash function as a whole is as well. In multi-block communications, a chain is created by using the “intermediate hash” the result of processing one block as an input for the subsequent block.
Security of SHA-2
The majority of applications that need a secure hash algorithm are advised to use the SHA-2 family of algorithms as they are usually regarded as secure. Despite extensive scholarly investigation, no significant vulnerabilities have been found. There is a huge margin of safety since, although collisions have been discovered by researchers, they have only occurred in drastically shortened versions of the algorithms (SHA-512, for example, 27 cycles as opposed to the actual 80 rounds). SHA-512/224 or SHA-512/256 are recommended because of their truncation characteristic in some situations when length extension attacks are a problem.
Alternatives and Future Outlook
NIST published SHA-3, a more secure family of algorithms, in 2015. It hasn’t been widely adopted despite being widely thought to be more secure than SHA-2 since SHA-2 algorithms still have a significant safety buffer and a major changeover isn’t urgently needed. As technology advances and a switch to even more powerful hashing algorithms becomes necessary, SHA-3 is a suitable substitute.
Compatibility and Transition Challenges
Although SHA-2 offers security benefits, the switch has been difficult, mostly because to backward compatibility problems with older apps and operating systems. SHA-2 is not supported by Windows XP Service Pack 2 or below, for example. To win over Windows-based devices, website owners needed new SHA-2 certificates to replace obsolete SHA-1 certificates that expired on January 1, 2017. For older systems, software, and hardware (such game consoles and embedded devices) that use hard-coded certificates, migration must be planned carefully. Windows Crypto Library and OpenSSL support SHA-2, making the switch easy for systems that utilize them.
Implementation and Performance
SHA-2 methods are made to divide the hash computation into two parts: a digest component that computes hash values repeatedly, and a pre-processing part that handles padding and dividing messages into fixed-size blocks. When linked via streams (FIFOs), these two components can function independently in parallel. As an example, SHA-256 processes 512 bits in 68 cycles at 314.36MHz, whereas SHA-512 processes 1024 bits in 84 cycles at 323.31MHz. These variations differ in terms of hardware resource utilization and performance metrics, including bits processed per cycle and clock frequency. SHA-2 primitives can be clustered to increase throughput by using message-level parallelism.
Advantages of SHA-2
Enhanced Security over Predecessors: With a greater level of security, SHA-2 was created to replace the less secure SHA-1 algorithm. It is not affected by the mathematical flaws in SHA-1. This is significant because effective attacks against SHA-1 became possible for government organisations, which led to NIST gradually withdrawing its support for SHA-1 by 2010.
Collision Resistance: SHA-2, a cryptographic hash algorithm, cannot find two messages with the same digest. Security requires “collision resistance” because collisions can undermine authentication systems, allowing attackers to sign a bogus contract with the same hash.
One-Way Function: SHA-2 is a one-way function, which means that with the methods and technology available today, it is almost difficult to determine an input from its hash alone. The foundation of internet security is this characteristic.
Variety of Hash Lengths and Strengths: The SHA-2 family has six distinct functions that generate hashes of 224, 256, 384, or 512 bits: SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, and SHA-512/256. In general, longer hash lengths offer better collision resistance. Of them, SHA-256 and SHA-512 are the most widely utilized.
Resistance to Length Extension Attacks (for truncated versions): Because SHA-512/224 and SHA-512/256 hashes are truncated that is, just the leftmost bits are retained while the rest are discarded they are very beneficial. These particular variations are guaranteed to lack enough information for length extension attacks due to this truncation. Fraudulent authentication might result from such attacks, which enable an attacker to replicate a digital signature without knowing a secret value.
Widespread Adoption and Use in Key Security Protocols: SHA-2 algorithms are widely employed in many security mechanisms that safeguard everyday internet communications. Among them are:
- Transport Layer Security (TLS) feature is present on https:// webpages.
- Internet Protocol Security (IPSec) is a common VPN feature.
- Email encryption solutions include Secure/Multipurpose Internet Mail Extensions (S/MIME) and Pretty Good Privacy (PGP).
- Secure Shell (SSH) allows file transfers and remote computer access.
- Since 2015, NIST has urged all federal entities to use them. They are also needed for blockchain technologies like Bitcoin’s proof-of-work function to authenticate data and prove its integrity.
Good Performance Characteristics: SHA-2 algorithms can take use of parallel processing to increase efficiency and are intended to be quick to calculate. SHA-256 processes 512 bits every 68 cycles at 314.36MHz, whereas SHA-512 processes 1024 bits per 84 cycles at 323.31MHz. This is an example of how performance differs across versions. Message-level parallelism can be used to cluster several instances in order to increase throughput.
Still Considered Secure: The SHA-2 family is advised for the majority of applications and is usually regarded as secure, even though it was created some time ago. Researchers have discovered collisions, but only in drastically shortened versions of the algorithms (SHA-512, for example, 27 cycles instead of the full 80 rounds), suggesting a large margin of safety.
Disadvantages of SHA-2
Backward Compatibility Issues: One drawback is that certain obsolete programs and operating systems don’t support SHA-2. Windows XP Service Pack 2 and lower don’t support SHA-2. Users with obsolete operating systems may have trouble seeing websites utilising SHA-2.
Transition Challenges for Legacy Systems: Enterprises with legacy systems that establish SSL connections and software and hardware (such as game consoles, phones, and embedded devices) that use hard-coded certificates need well-tested migration plans to avoid major disruptions or technology breakdown when switching to SHA-2. Software without SHA-2 encryption may need updates.
Increased Computational Resources for Longer Hashes: There is a trade-off between greater hash lengths and improved collision resistance: the longer the hash, the more computer resources it requires and the longer it takes to calculate.
Not Specifically Tailored for Password Hashing: While SHA-2 hash algorithms are occasionally employed for password hashing, this is not regarded as a recommended practice. For increased security, it is preferable to utilise programs like bcrypt that are designed especially for password hashing.
SHA-3 Exists as a More Secure Alternative: NIST published SHA-3, a more secure family of algorithms, in 2015, however SHA-2 is still regarded as being extremely safe. Although SHA-3 is widely thought to be more secure, its uptake has been slow since SHA-2 algorithms still have a significant safety buffer and a major switch isn’t urgently needed just now.