Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/Documentation/digsig.txt

  1 Digital Signature Verification API
  2 
  3 CONTENTS
  4 
  5 1. Introduction
  6 2. API
  7 3. User-space utilities
  8 
  9 
 10 1. Introduction
 11 
 12 Digital signature verification API provides a method to verify digital signature.
 13 Currently digital signatures are used by the IMA/EVM integrity protection subsystem.
 14 
 15 Digital signature verification is implemented using cut-down kernel port of
 16 GnuPG multi-precision integers (MPI) library. The kernel port provides
 17 memory allocation errors handling, has been refactored according to kernel
 18 coding style, and checkpatch.pl reported errors and warnings have been fixed.
 19 
 20 Public key and signature consist of header and MPIs.
 21 
 22 struct pubkey_hdr {
 23         uint8_t         version;        /* key format version */
 24         time_t          timestamp;      /* key made, always 0 for now */
 25         uint8_t         algo;
 26         uint8_t         nmpi;
 27         char            mpi[0];
 28 } __packed;
 29 
 30 struct signature_hdr {
 31         uint8_t         version;        /* signature format version */
 32         time_t          timestamp;      /* signature made */
 33         uint8_t         algo;
 34         uint8_t         hash;
 35         uint8_t         keyid[8];
 36         uint8_t         nmpi;
 37         char            mpi[0];
 38 } __packed;
 39 
 40 keyid equals to SHA1[12-19] over the total key content.
 41 Signature header is used as an input to generate a signature.
 42 Such approach insures that key or signature header could not be changed.
 43 It protects timestamp from been changed and can be used for rollback
 44 protection.
 45 
 46 2. API
 47 
 48 API currently includes only 1 function:
 49 
 50         digsig_verify() - digital signature verification with public key
 51 
 52 
 53 /**
 54  * digsig_verify() - digital signature verification with public key
 55  * @keyring:    keyring to search key in
 56  * @sig:        digital signature
 57  * @sigen:      length of the signature
 58  * @data:       data
 59  * @datalen:    length of the data
 60  * @return:     0 on success, -EINVAL otherwise
 61  *
 62  * Verifies data integrity against digital signature.
 63  * Currently only RSA is supported.
 64  * Normally hash of the content is used as a data for this function.
 65  *
 66  */
 67 int digsig_verify(struct key *keyring, const char *sig, int siglen,
 68                                                 const char *data, int datalen);
 69 
 70 3. User-space utilities
 71 
 72 The signing and key management utilities evm-utils provide functionality
 73 to generate signatures, to load keys into the kernel keyring.
 74 Keys can be in PEM or converted to the kernel format.
 75 When the key is added to the kernel keyring, the keyid defines the name
 76 of the key: 5D2B05FC633EE3E8 in the example bellow.
 77 
 78 Here is example output of the keyctl utility.
 79 
 80 $ keyctl show
 81 Session Keyring
 82        -3 --alswrv      0     0  keyring: _ses
 83 603976250 --alswrv      0    -1   \_ keyring: _uid.0
 84 817777377 --alswrv      0     0       \_ user: kmk
 85 891974900 --alswrv      0     0       \_ encrypted: evm-key
 86 170323636 --alswrv      0     0       \_ keyring: _module
 87 548221616 --alswrv      0     0       \_ keyring: _ima
 88 128198054 --alswrv      0     0       \_ keyring: _evm
 89 
 90 $ keyctl list 128198054
 91 1 key in keyring:
 92 620789745: --alswrv     0     0 user: 5D2B05FC633EE3E8
 93 
 94 
 95 Dmitry Kasatkin
 96 06.10.2011

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us