pdf-utils

PDF Utils

A collection of lightweight Rust crates for parsing, extracting text, and verifying digital signatures in PDF documents. Designed specifically for zero-knowledge environments and constrained systems.

🎯 Design Philosophy

This repository provides minimal, dependency-light Rust crates for working with PDFs in zero-knowledge friendly environments. All core logic avoids heavy dependencies like lopdf, flate2, and openssl, making it suitable for:

• Zero-knowledge virtual machines (e.g., SP1, Risc0)
• WASM targets for web applications
• Constrained, auditable environments requiring minimal attack surface
• Blockchain applications needing PDF verification

📦 Crates Overview

extractor - PDF Text Extraction

Extracts plain text from PDF files with support for:

• Common font encodings (ToUnicode, Differences, built-in maps)
• CID fonts and glyph name mapping
• Minimal PDF parsing with no external PDF libraries
• Support for StandardEncoding, WinAnsiEncoding, MacRomanEncoding, and PDFDocEncoding

signature-validator - Digital Signature Verification

Verifies embedded digital signatures in PDFs using:

• Raw PKCS#7/CMS parsing
• Rust ASN.1 decoding
• RSA/SHA1, SHA256, SHA384, and SHA512 digest verification
• Content integrity and signature authenticity checks

core - Combined PDF Verification

Combines extractor and signature-validator to:

• Validate that specific text appears in a signed PDF
• Check its exact byte offset on a given page
• Return boolean results for use in proofs or UIs
• Provide unified interface for PDF verification

wasm - WebAssembly Interface

A thin WebAssembly wrapper around the core crate:

• Browser-compatible PDF verification
• JavaScript/TypeScript bindings
• Base64 PDF input/output support

🚀 Quick Start

Basic Text Extraction

use extractor::extract_text;

let pdf_bytes = std::fs::read("document.pdf")?;
let pages = extract_text(pdf_bytes)?;
println!("Page 1: {}", pages[0]);

Signature Verification

use signature_validator::verify_pdf_signature;

let pdf_bytes = std::fs::read("signed_document.pdf")?;
let is_valid = verify_pdf_signature(&pdf_bytes)?;
println!("Signature valid: {}", is_valid);

Combined Verification

use core::verify_text;

let pdf_bytes = std::fs::read("document.pdf")?;
let result = verify_text(pdf_bytes, 0, "Sample Text", 100)?;
println!("Text found at position: {}", result.substring_matches);

🧪 Testing

All crates share the same workspace. Run the public tests with:

cargo test

Some crates have additional private tests that rely on PDF files not included in this repository. To run them, add the private_tests feature:

cargo test --features private_tests

Run tests for a specific crate:

cargo test -p extractor
cargo test -p signature-validator
cargo test -p core
cargo test -p wasm

📋 Feature Support

Feature	Support
Text Extraction	✅
Font Encoding	✅
Digital Signatures	✅
PKCS#7/CMS	✅
Multi-page Documents	✅
Compressed Streams	✅
Position-based Matching	✅
Combined Verification	✅
WebAssembly	✅
Image Extraction	❌
Form Field Processing	❌
ECDSA Signatures	❌
Certificate Chain Validation	❌
Timestamp Verification	❌
Multiple Signatures	❌
Complex Layout Analysis	❌

🔧 Dependencies

• Minimal external dependencies - Only essential crates like miniz_oxide, rsa, sha2
• No heavy PDF libraries - Custom lightweight PDF parser
• Zero-knowledge friendly - All algorithms compatible with ZK-VMs
• WASM compatible - All crates compile to WebAssembly

📚 Documentation

Each crate has detailed documentation:

• Extractor Documentation
• Signature Validator Documentation
• Core Documentation
• WASM Documentation

🤝 Contributing

This project is designed for zero-knowledge applications. When contributing:

• Keep dependencies minimal
• Ensure ZK-VM compatibility
• Add tests for new features
• Document any breaking changes

📄 License

This project is licensed under the same terms as the parent repository.