Glossary

Key terms used throughout this documentation. If you’re coming from the MPQ/3.3.5a modding scene, pay attention to the “MPQ Equivalent” notes.

Content Identification

Content Key (CKey)

MD5 hash of a file’s uncompressed content. Used to identify files regardless of how they’re compressed or stored.

• Size: 16 bytes (128 bits)
• MPQ Equivalent: Similar to how MPQ uses filenames, but content-based
• Example: a1b2c3d4e5f6... (32 hex characters)

Encoding Key (EKey)

MD5 hash of a file’s compressed/encoded BLTE data. Used to locate files on CDN and in archives.

• Size: 16 bytes (128 bits)
• Relationship: CKey → Encoding File → EKey
• Example: Files with identical content share a CKey but may have different EKeys

FileDataID (FDID)

Numeric identifier for a file, persistent across game versions. Replaced filename-based lookups in WoW 8.0+.

• Size: 4 bytes (32-bit integer)
• Range: 0 to ~4 million (as of 2024)
• MPQ Equivalent: None - MPQ used filenames exclusively
• Example: 1234567 refers to a specific texture, model, or data file

Name Hash

Jenkins96 hash of a file’s path. Used in older builds (pre-8.0) to look up files by name.

• Algorithm: Jenkins96 (lookup3)
• MPQ Equivalent: Similar to MPQ’s hash table for filename lookup
• Note: Deprecated in favor of FileDataID in modern builds

File Formats

BLTE (Block Table Encoded)

Container format that wraps all CASC content. Provides compression and optional encryption.

• MPQ Equivalent: Similar to MPQ’s sector-based compression
• Key difference: BLTE supports multiple compression algorithms per file
• Compression: None, zlib, LZMA, LZ4, Zstd
• Encryption: Salsa20, ARC4 (older builds)

Encoding File

Maps CKeys to EKeys. The central lookup table for content resolution.

• Purpose: Find where a file’s compressed data lives
• MPQ Equivalent: None - MPQ stored files directly by name

Root File

Maps FileDataIDs (or name hashes) to CKeys. The entry point for file lookup.

• Purpose: Find what content hash a file has
• MPQ Equivalent: Combines MPQ’s hash table and block table functions
• Contains: FileDataID, locale flags, content flags, CKey

Install Manifest

Lists files required for a minimal installation (enough to launch the game).

• Purpose: Prioritize essential files for streaming installs
• MPQ Equivalent: None - MPQ required full downloads

Download Manifest

Prioritizes files for background downloading after initial install.

• Purpose: Order non-essential downloads by importance
• MPQ Equivalent: None

Storage Concepts

Archive

Large file containing many compressed files, identified by EKey.

• CDN archives: ~256 MB bundles served via HTTP
• Local archives: data.xxx files in the Data folder
• MPQ Equivalent: Similar to .mpq files, but content-addressed

Archive Index

Maps EKeys to offsets within an archive file.

• CDN index: .index file paired with each archive
• Local index: .idx files in Data/indices/
• MPQ Equivalent: Similar to MPQ’s block table

Archive Group

Combined index covering multiple archives. Optimization for faster lookups.

• Location: Generated locally by the client from downloaded archive indices
• Purpose: Single lookup instead of checking each archive index
• Note: Never downloaded from CDN - always client-generated

CASC (Content Addressable Storage Container)

The local storage system. Everything is identified by content hash.

• MPQ Equivalent: Replaces MPQ archives entirely
• Key difference: Files found by hash, not by name

Network Concepts

CDN (Content Delivery Network)

Servers that host game content. Blizzard uses Akamai, Level3, and others.

• Structure: https://{cdn}/{product}/{type}/{hash[:2]}/{hash[2:4]}/{hash}
• Types: config, data, patch

Ribbit

Protocol for querying product versions and CDN information.

• Port: 1119 (TCP) or HTTP
• Purpose: Discover what versions exist and where to download them
• MPQ Equivalent: None - MPQ versions were distributed manually

Agent

Local HTTP service (port 1120) that manages downloads and installations.

• Purpose: Background downloading, installation management
• MPQ Equivalent: None - MPQ required manual patching

Configuration

Build Config

Per-build settings including root/encoding file hashes and encryption keys.

• Location: CDN /config/{hash}
• Contains: Root CKey, encoding CKey, patch info, VFS info

CDN Config

Lists available CDN servers and archive hashes.

• Location: CDN /config/{hash}
• Contains: Archive list, server URLs, file groups

Product Config

Product-wide settings spanning multiple builds.

• Location: CDN /config/{hash}
• Contains: Decryption keys, feature flags

Encryption

TACT Key

Encryption key for protected content. Named keys are published, unnamed are secret.

• Size: 16 bytes
• Algorithm: Used with Salsa20 stream cipher
• Source: Community-maintained key databases

Salsa20

Stream cipher used for content encryption in modern builds.

• Key size: 256 bits (16-byte key + 16-byte name as nonce)
• Replaces: ARC4 (used in older builds)

MPQ to CASC Quick Reference

See Also

• NGDP on wowdev.wiki
• CASC on wowdev.wiki
• TACT on wowdev.wiki