fsverity - Man Page

Compute the fs-verity digest of the given file(s). This is mainly intended to used in preparation for signing the digest. In some cases fsverity sign can be used instead to digest and sign the file in one step.

Options accepted by fsverity digest:

--block-size=BLOCK_SIZE

The Merkle tree block size (in bytes) to use. This must be a power of 2 and at least twice the size of the hash values.

Note that the Linux kernel implementations of fs-verity place further restrictions on the Merkle tree block size. Linux v6.2 and earlier require that the Merkle tree block size be equal to both the system page size and the filesystem block size. These values are often 4096. Linux v6.3 and later are more flexible; they require that the Merkle tree block size be a power of 2 that is greater than or equal to 1024 and less than or equal to the system page size and the filesystem block size. The default value of this option is 4096.

--compact

When printing the file digest, only print the actual digest hex string; don’t print the algorithm name and filename.

--for-builtin-sig

Format the file digest in a way that is compatible with the Linux kernel’s fs-verity built-in signature verification support. This means formatting it as a struct fsverity_formatted_digest. Use this option if you are using built-in signatures but are not using fsverity sign to do the signing.

--hash-alg=HASH_ALG

The hash algorithm to use to build the Merkle tree. Valid options are sha256 and sha512. Default is sha256.

--out-merkle-tree=FILE

Write the computed Merkle tree to the given file. The Merkle tree layout will be the same as that used by the Linux kernel’s FS_IOC_READ_VERITY_METADATA ioctl.

Normally this option isn’t useful, but it can be needed in cases where the fs-verity metadata needs to be consumed by something other than one of the native Linux kernel implementations of fs-verity. This is not needed for file signing.

--out-descriptor=FILE

Write the computed fs-verity descriptor to the given file.

Normally this option isn’t useful, but it can be needed in cases where the fs-verity metadata needs to be consumed by something other than one of the native Linux kernel implementations of fs-verity. This is not needed for file signing.

--salt=SALT

The salt to use in the Merkle tree, as a hex string. The salt is a value that is prepended to every hashed block; it can be used to personalize the hashing for a particular file or device. The default is no salt.

Dump the fs-verity metadata of the given file. The file must have fs-verity enabled, and the filesystem must support the FS_IOC_READ_VERITY_METADATA ioctl (it was added in Linux v5.12). This subcommand normally isn’t useful, but it can be useful in cases where a userspace server program is serving a verity file to a client which implements fs-verity compatible verification.

TYPE may be “merkle_tree”, “descriptor”, or “signature”, indicating the type of metadata to dump. “signature” refers to the built-in signature, if present; userspace-managed signatures will not be included.

Options accepted by fsverity dump_metadata:

--length=LENGTH

Length in bytes to dump from the specified metadata item. Only accepted in combination with --offset.

--offset=offset

Offset in bytes into the specified metadata item at which to start dumping. Only accepted in combination with --length.

Enable fs-verity on the specified file. This will only work if the filesystem supports fs-verity.

Options accepted by fsverity enable:

--block-size=BLOCK_SIZE

Same as for fsverity digest.

--hash-alg=HASH_ALG

Same as for fsverity digest.

--salt=SALT

Same as for fsverity digest.

--signature=SIGFILE

Specifies the built-in signature to apply to the file. SIGFILE must be a file that contains the signature in PKCS#7 DER format, e.g. as produced by the fsverity sign command.

Note that this option is only needed if the Linux kernel’s fs-verity built-in signature verification support is being used. It is not needed if the signatures will be verified in userspace, as in that case the signatures should be stored separately.

Display the fs-verity digest of the given file(s). The files must have fs-verity enabled. The output will be the same as fsverity digest with the appropriate parameters, but fsverity measure will take constant time for each file regardless of the size of the file.

fsverity measure does not accept any options.

Sign the given file for fs-verity, in a way that is compatible with the Linux kernel’s fs-verity built-in signature verification support. The signature will be written to OUT_SIGFILE in PKCS#7 DER format.

The private key can be specified either by key file or by PKCS#11 token. To use a key file, provide --key and optionally --cert. To use a PKCS#11 token, provide --pkcs11-engine, --pkcs11-module, --cert, and optionally --pkcs11-keyid. PKCS#11 token support is unavailable when fsverity-utils was built with BoringSSL rather than OpenSSL.

fsverity sign should only be used if you need compatibility with fs-verity built-in signatures. It is not the only way to do signatures with fs-verity. For more information, see the fsverity-utils README.

Options accepted by fsverity sign:

--block-size=BLOCK_SIZE

Same as for fsverity digest.

--cert=CERTFILE

Specifies the file that contains the certificate, in PEM format. This option is required if KEYFILE contains only the private key and not also the certificate, or if a PKCS#11 token is used.

--hash-alg=HASH_ALG

Same as for fsverity digest.

--key=KEYFILE

Specifies the file that contains the private key, in PEM format. This option is required when not using a PKCS#11 token.

--out-descriptor=FILE

Same as for fsverity digest.

--out-merkle-tree=FILE

Same as for fsverity digest.

--pkcs11-engine=SOFILE

Specifies the path to the OpenSSL PKCS#11 engine file. This typically will be a path to the libp11 .so file. This option is required when using a PKCS#11 token.

--pkcs11-keyid=KEYID

Specifies the key identifier in the form of a PKCS#11 URI. If not provided, the default key associated with the token is used. This option is only applicable when using a PKCS#11 token.

--pkcs11-module=SOFILE

Specifies the path to the PKCS#11 token-specific module library. This option is required when using a PKCS#11 token.

--salt=SALT

Same as for fsverity digest.