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ERROR_EFS_ALG_BLOB_TOO_BIG
The destination cannot hold the source EFS algorithm information
EFS metadata carries the cryptographic information needed to protect and recover the file-encryption key. This error can appear during copy, restore, or migration when the destination implementation allocates a smaller key-information buffer or does not support the source format.
Do not truncate the algorithm blob. A shortened structure may make the encrypted file permanently unusable. Preserve the source and use a compatible system, a raw EFS backup/restore path, or an authorized decrypt-and-reencrypt migration.
What to inspect
- Source and destination Windows versions, file systems, and encryption providers.
- Any backup tool, filter driver, or cross-platform NTFS implementation that transforms EFS metadata.
- Whether the complete raw stream was preserved without fixed-size assumptions.
- Successful decryption of a test copy before deleting the original.
References
- Microsoft: Encrypted-file backup and restore
- Microsoft Open Specifications: EFS overview
- libfsntfs: NTFS format documentation
- NTFS-3G: ntfsdecrypt
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