API Security•Feb 26, 2026•6 min read

SHA-1 vs SHA-256 — Key Differences, Security & When to Use Each

S

Shreya Srivastava

Content Team

Tags:sha1 vs sha256 sha-1 vs sha-256 sha1 versus sha256 difference between sha1 and sha256 sha1 or sha256

Updated on: February 2026

SHA-1 vs SHA-256: Quick Summary

SHA-1 and SHA-256 are both cryptographic hash functions from the SHA (Secure Hash Algorithm) family, but they differ significantly in security strength and output size. SHA-1 is now considered broken for security purposes, while SHA-256 remains secure. Here's a quick comparison:

Feature	SHA-1	SHA-256
Algorithm Family	SHA-1	SHA-2
Output Size	160 bits (40 hex chars)	256 bits (64 hex chars)
Security Status	Broken — collision attacks demonstrated	Secure — no known practical attacks
Speed	Faster	Slower (~30-40% more computation)
Collision Resistance	Weak (2^63 operations)	Strong (2^128 operations)
Industry Status	Deprecated by NIST, browsers, and CAs	Current standard, widely mandated
Use in TLS/SSL	No longer accepted	Standard
Git	Default (legacy)	Optional (SHA-256 mode)

What Is SHA-1?

SHA-1 (Secure Hash Algorithm 1) is a cryptographic hash function that produces a 160-bit (20-byte) hash value, typically rendered as a 40-character hexadecimal string. Designed by the NSA and published by NIST in 1995, SHA-1 was the standard hashing algorithm for over a decade.

Example SHA-1 hash:

Input:  "Hello World"
SHA-1:  0a4d55a8d778e5022fab701977c5d840bbc486d0

SHA-1 was widely used for:

SSL/TLS certificates
Digital signatures
Git version control (commit and object hashing)
File integrity verification
HMAC-based authentication

However, SHA-1 is now considered cryptographically broken. In 2017, Google and CWI Amsterdam demonstrated the first practical SHA-1 collision attack (SHAttered), producing two different PDF files with the same SHA-1 hash. The attack cost approximately $110,000 in cloud computing resources — well within reach of well-funded attackers.

You can generate SHA-1 hashes for testing and legacy compatibility using Qodex's free SHA-1 Hash Generator.

What Is SHA-256?

SHA-256 (Secure Hash Algorithm 256) is a cryptographic hash function from the SHA-2 family that produces a 256-bit (32-byte) hash value, rendered as a 64-character hexadecimal string. Published by NIST in 2001, SHA-256 is currently the most widely used hash function for security applications.

Example SHA-256 hash:

Input:  "Hello World"
SHA-256: a591a6d40bf420404a011733cfb7b190d62c65bf0bcda32b57b277d9ad9f146e

SHA-256 is used for:

TLS/SSL certificates — the standard since 2017 when CAs stopped issuing SHA-1 certificates
Digital signatures — code signing, document signing, S/MIME
Blockchain — Bitcoin and many cryptocurrencies use SHA-256 for proof-of-work and transaction hashing
Password storage — as part of PBKDF2, bcrypt, or scrypt key derivation
File integrity — verifying downloads, package checksums
API security — HMAC-SHA256 for API authentication and webhook signatures

No practical attacks against SHA-256 have been demonstrated. The theoretical collision resistance of 2^128 operations makes brute-force attacks infeasible with current and foreseeable technology.

Generate SHA-256 hashes instantly with Qodex's free SHA-256 Hash Generator.

Key Differences Between SHA-1 and SHA-256

1. Security Strength

This is the most critical difference. SHA-1's collision resistance has been practically broken — attackers can create two different inputs that produce the same hash. SHA-256 has no known practical vulnerabilities. For any security-sensitive application, SHA-256 is the minimum acceptable choice.

2. Output Size

SHA-1 produces a 160-bit hash (40 hex characters), while SHA-256 produces a 256-bit hash (64 hex characters). The larger output provides exponentially more possible hash values, making collisions astronomically unlikely.

3. Computation Speed

SHA-1 is approximately 30-40% faster than SHA-256 because it processes smaller blocks and performs fewer rounds of computation. However, this speed advantage is also a security disadvantage — faster hashing means faster brute-force attacks. For password hashing, slower is actually better.

4. Algorithm Design

SHA-1 uses 80 rounds of operations on 512-bit blocks. SHA-256 uses 64 rounds but with more complex operations on 512-bit blocks, producing a significantly more secure output through better diffusion and confusion properties.

5. Industry Adoption

SHA-1 has been deprecated across the industry:

Browsers reject SHA-1 signed certificates (since 2017)
Certificate Authorities stopped issuing SHA-1 certificates
NIST deprecated SHA-1 for digital signatures
PCI DSS requires SHA-256 or stronger

SHA-256 is mandated by virtually all modern security standards and compliance frameworks.

Performance Comparison

Metric	SHA-1	SHA-256
Hash Speed (software)	~1000 MB/s	~650 MB/s
Relative Speed	~30-40% faster	Baseline
Hardware Acceleration	SHA-NI (Intel/AMD)	SHA-NI (Intel/AMD), ARM SHA2
Hash Output Size	20 bytes	32 bytes
Storage Overhead	Lower	60% more storage per hash

With modern hardware acceleration (Intel SHA-NI extensions), the performance gap narrows significantly. Most modern processors include dedicated SHA-256 instructions that bring its throughput close to SHA-1 speeds.

For most applications, the performance difference between SHA-1 and SHA-256 is negligible compared to network latency, disk I/O, and other bottlenecks. Don't sacrifice security for a minor speed improvement.

When to Use SHA-1 (Legacy Only)

SHA-1 should not be used for any new security applications. The only acceptable uses are:

Git compatibility — Git uses SHA-1 by default for object hashing (though Git 2.29+ supports SHA-256 mode)
Non-security checksums — when you only need to detect accidental corruption, not adversarial tampering (though SHA-256 is still preferred)
Legacy system compatibility — when interacting with systems that only support SHA-1 (with a plan to migrate)
HMAC-SHA1 — HMAC construction is still considered secure even with SHA-1, because the attack model is different (though HMAC-SHA256 is preferred)

If you're maintaining legacy systems that use SHA-1, prioritize migrating to SHA-256 as part of your security roadmap.

When to Use SHA-256

SHA-256 should be your default choice for virtually all hashing needs:

TLS/SSL certificates — required by all certificate authorities and browsers
Digital signatures — code signing, document signing, S/MIME
API authentication — HMAC-SHA256 for API security, webhook verification, JWT signing
File integrity — verifying downloads, container images, package checksums
Password hashing — as input to key derivation functions like PBKDF2 or Argon2
Blockchain and cryptographic protocols — Bitcoin, Ethereum (for Merkle trees), and many cryptographic applications
Compliance — PCI DSS, HIPAA, SOC 2, and other frameworks require SHA-256 or stronger

For applications requiring even stronger hashing, consider SHA-512, which provides 512-bit output and can be faster than SHA-256 on 64-bit processors.

SHA-1, SHA-256, and API Security

Hash functions play a critical role in API security:

Webhook signatures — services like GitHub and Stripe use HMAC-SHA256 to sign webhook payloads so receivers can verify authenticity
API key hashing — API keys should be stored as SHA-256 hashes, never in plaintext
Request integrity — hashing request bodies ensures they haven't been tampered with in transit
Token generation — JWT tokens commonly use HMAC-SHA256 (HS256) or RSA-SHA256 (RS256) signatures

If you're building or testing APIs, always use SHA-256 or stronger for any cryptographic operations. Qodex.ai automatically tests for OWASP Top 10 API security vulnerabilities, including weak cryptographic implementations.

Frequently Asked Questions

Is SHA-1 still safe to use?

No, SHA-1 is not safe for security applications. Collision attacks have been demonstrated practically (Google's SHAttered attack in 2017), and the cost of attacks continues to drop. SHA-1 is deprecated by NIST, all major browsers, certificate authorities, and compliance frameworks. Use SHA-256 or stronger for all security-sensitive applications.

Why does Git still use SHA-1?

Git adopted SHA-1 in 2005 when it was still considered secure. Migrating a version control system's core hashing algorithm is a massive undertaking that affects every repository. Git 2.29 (released 2020) added experimental SHA-256 support, and the migration is ongoing. For Git's use case (detecting accidental corruption), SHA-1 collisions are extremely unlikely in practice, though targeted attacks are possible.

Is SHA-256 slower than SHA-1?

Yes, SHA-256 is approximately 30-40% slower than SHA-1 in pure software implementations. However, modern CPUs with SHA-NI (Intel/AMD) or SHA2 (ARM) hardware acceleration significantly close this gap. For most applications, the performance difference is negligible compared to other bottlenecks like network I/O.

What is a SHA-256 collision?

A collision occurs when two different inputs produce the same hash output. For SHA-256, finding a collision would require approximately 2^128 operations — a number so large that it's considered computationally infeasible with any current or foreseeable technology. No SHA-256 collision has ever been found.

Should I use SHA-256 or SHA-512?

Both are secure. SHA-256 is more commonly used and widely supported. SHA-512 produces a larger output (512 bits) and can actually be faster than SHA-256 on 64-bit processors because its internal operations use 64-bit words. Choose SHA-512 when you need extra security margin or when running on 64-bit hardware. For most applications, SHA-256 is sufficient.

Can you reverse a SHA-256 hash?

No. SHA-256 is a one-way function — you cannot mathematically reverse it to find the original input. The only way to "crack" a hash is through brute-force (trying all possible inputs) or using precomputed rainbow tables. This is why SHA-256 is used for password hashing (combined with salting) and digital signatures.