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-Digital Signature Verification API
-
-CONTENTS
-
-1. Introduction
-2. API
-3. User-space utilities
-
-
-1. Introduction
-
-Digital signature verification API provides a method to verify digital signature.
-Currently digital signatures are used by the IMA/EVM integrity protection subsystem.
-
-Digital signature verification is implemented using cut-down kernel port of
-GnuPG multi-precision integers (MPI) library. The kernel port provides
-memory allocation errors handling, has been refactored according to kernel
-coding style, and checkpatch.pl reported errors and warnings have been fixed.
-
-Public key and signature consist of header and MPIs.
-
-struct pubkey_hdr {
- uint8_t version; /* key format version */
- time_t timestamp; /* key made, always 0 for now */
- uint8_t algo;
- uint8_t nmpi;
- char mpi[0];
-} __packed;
-
-struct signature_hdr {
- uint8_t version; /* signature format version */
- time_t timestamp; /* signature made */
- uint8_t algo;
- uint8_t hash;
- uint8_t keyid[8];
- uint8_t nmpi;
- char mpi[0];
-} __packed;
-
-keyid equals to SHA1[12-19] over the total key content.
-Signature header is used as an input to generate a signature.
-Such approach insures that key or signature header could not be changed.
-It protects timestamp from been changed and can be used for rollback
-protection.
-
-2. API
-
-API currently includes only 1 function:
-
- digsig_verify() - digital signature verification with public key
-
-
-/**
- * digsig_verify() - digital signature verification with public key
- * @keyring: keyring to search key in
- * @sig: digital signature
- * @sigen: length of the signature
- * @data: data
- * @datalen: length of the data
- * @return: 0 on success, -EINVAL otherwise
- *
- * Verifies data integrity against digital signature.
- * Currently only RSA is supported.
- * Normally hash of the content is used as a data for this function.
- *
- */
-int digsig_verify(struct key *keyring, const char *sig, int siglen,
- const char *data, int datalen);
-
-3. User-space utilities
-
-The signing and key management utilities evm-utils provide functionality
-to generate signatures, to load keys into the kernel keyring.
-Keys can be in PEM or converted to the kernel format.
-When the key is added to the kernel keyring, the keyid defines the name
-of the key: 5D2B05FC633EE3E8 in the example bellow.
-
-Here is example output of the keyctl utility.
-
-$ keyctl show
-Session Keyring
- -3 --alswrv 0 0 keyring: _ses
-603976250 --alswrv 0 -1 \_ keyring: _uid.0
-817777377 --alswrv 0 0 \_ user: kmk
-891974900 --alswrv 0 0 \_ encrypted: evm-key
-170323636 --alswrv 0 0 \_ keyring: _module
-548221616 --alswrv 0 0 \_ keyring: _ima
-128198054 --alswrv 0 0 \_ keyring: _evm
-
-$ keyctl list 128198054
-1 key in keyring:
-620789745: --alswrv 0 0 user: 5D2B05FC633EE3E8
-
-
-Dmitry Kasatkin
-06.10.2011