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