diff options
Diffstat (limited to 'Documentation/security')
| -rw-r--r-- | Documentation/security/keys-ecryptfs.txt | 68 | ||||
| -rw-r--r-- | Documentation/security/keys-trusted-encrypted.txt | 53 |
2 files changed, 102 insertions, 19 deletions
diff --git a/Documentation/security/keys-ecryptfs.txt b/Documentation/security/keys-ecryptfs.txt new file mode 100644 index 0000000..c3bbeba --- /dev/null +++ b/Documentation/security/keys-ecryptfs.txt @@ -0,0 +1,68 @@ + Encrypted keys for the eCryptfs filesystem + +ECryptfs is a stacked filesystem which transparently encrypts and decrypts each +file using a randomly generated File Encryption Key (FEK). + +Each FEK is in turn encrypted with a File Encryption Key Encryption Key (FEFEK) +either in kernel space or in user space with a daemon called 'ecryptfsd'. In +the former case the operation is performed directly by the kernel CryptoAPI +using a key, the FEFEK, derived from a user prompted passphrase; in the latter +the FEK is encrypted by 'ecryptfsd' with the help of external libraries in order +to support other mechanisms like public key cryptography, PKCS#11 and TPM based +operations. + +The data structure defined by eCryptfs to contain information required for the +FEK decryption is called authentication token and, currently, can be stored in a +kernel key of the 'user' type, inserted in the user's session specific keyring +by the userspace utility 'mount.ecryptfs' shipped with the package +'ecryptfs-utils'. + +The 'encrypted' key type has been extended with the introduction of the new +format 'ecryptfs' in order to be used in conjunction with the eCryptfs +filesystem. Encrypted keys of the newly introduced format store an +authentication token in its payload with a FEFEK randomly generated by the +kernel and protected by the parent master key. + +In order to avoid known-plaintext attacks, the datablob obtained through +commands 'keyctl print' or 'keyctl pipe' does not contain the overall +authentication token, which content is well known, but only the FEFEK in +encrypted form. + +The eCryptfs filesystem may really benefit from using encrypted keys in that the +required key can be securely generated by an Administrator and provided at boot +time after the unsealing of a 'trusted' key in order to perform the mount in a +controlled environment. Another advantage is that the key is not exposed to +threats of malicious software, because it is available in clear form only at +kernel level. + +Usage: + keyctl add encrypted name "new ecryptfs key-type:master-key-name keylen" ring + keyctl add encrypted name "load hex_blob" ring + keyctl update keyid "update key-type:master-key-name" + +name:= '<16 hexadecimal characters>' +key-type:= 'trusted' | 'user' +keylen:= 64 + + +Example of encrypted key usage with the eCryptfs filesystem: + +Create an encrypted key "1000100010001000" of length 64 bytes with format +'ecryptfs' and save it using a previously loaded user key "test": + + $ keyctl add encrypted 1000100010001000 "new ecryptfs user:test 64" @u + 19184530 + + $ keyctl print 19184530 + ecryptfs user:test 64 490045d4bfe48c99f0d465fbbbb79e7500da954178e2de0697 + dd85091f5450a0511219e9f7cd70dcd498038181466f78ac8d4c19504fcc72402bfc41c2 + f253a41b7507ccaa4b2b03fff19a69d1cc0b16e71746473f023a95488b6edfd86f7fdd40 + 9d292e4bacded1258880122dd553a661 + + $ keyctl pipe 19184530 > ecryptfs.blob + +Mount an eCryptfs filesystem using the created encrypted key "1000100010001000" +into the '/secret' directory: + + $ mount -i -t ecryptfs -oecryptfs_sig=1000100010001000,\ + ecryptfs_cipher=aes,ecryptfs_key_bytes=32 /secret /secret diff --git a/Documentation/security/keys-trusted-encrypted.txt b/Documentation/security/keys-trusted-encrypted.txt index 8fb79bc..c9e4855 100644 --- a/Documentation/security/keys-trusted-encrypted.txt +++ b/Documentation/security/keys-trusted-encrypted.txt @@ -53,12 +53,19 @@ they are only as secure as the user key encrypting them. The master user key should therefore be loaded in as secure a way as possible, preferably early in boot. +The decrypted portion of encrypted keys can contain either a simple symmetric +key or a more complex structure. The format of the more complex structure is +application specific, which is identified by 'format'. + Usage: - keyctl add encrypted name "new key-type:master-key-name keylen" ring - keyctl add encrypted name "load hex_blob" ring - keyctl update keyid "update key-type:master-key-name" + keyctl add encrypted name "new [format] key-type:master-key-name keylen" + ring + keyctl add encrypted name "load hex_blob" ring + keyctl update keyid "update key-type:master-key-name" + +format:= 'default | ecryptfs' +key-type:= 'trusted' | 'user' -where 'key-type' is either 'trusted' or 'user'. Examples of trusted and encrypted key usage: @@ -114,15 +121,25 @@ Reseal a trusted key under new pcr values: 7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8 -Create and save an encrypted key "evm" using the above trusted key "kmk": +The initial consumer of trusted keys is EVM, which at boot time needs a high +quality symmetric key for HMAC protection of file metadata. The use of a +trusted key provides strong guarantees that the EVM key has not been +compromised by a user level problem, and when sealed to specific boot PCR +values, protects against boot and offline attacks. Create and save an +encrypted key "evm" using the above trusted key "kmk": +option 1: omitting 'format' $ keyctl add encrypted evm "new trusted:kmk 32" @u 159771175 +option 2: explicitly defining 'format' as 'default' + $ keyctl add encrypted evm "new default trusted:kmk 32" @u + 159771175 + $ keyctl print 159771175 - trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382dbbc55 - be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e024717c64 - 5972dcb82ab2dde83376d82b2e3c09ffc + default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3 + 82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0 + 24717c64 5972dcb82ab2dde83376d82b2e3c09ffc $ keyctl pipe 159771175 > evm.blob @@ -132,14 +149,12 @@ Load an encrypted key "evm" from saved blob: 831684262 $ keyctl print 831684262 - trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382dbbc55 - be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e024717c64 - 5972dcb82ab2dde83376d82b2e3c09ffc - - -The initial consumer of trusted keys is EVM, which at boot time needs a high -quality symmetric key for HMAC protection of file metadata. The use of a -trusted key provides strong guarantees that the EVM key has not been -compromised by a user level problem, and when sealed to specific boot PCR -values, protects against boot and offline attacks. Other uses for trusted and -encrypted keys, such as for disk and file encryption are anticipated. + default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3 + 82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0 + 24717c64 5972dcb82ab2dde83376d82b2e3c09ffc + +Other uses for trusted and encrypted keys, such as for disk and file encryption +are anticipated. In particular the new format 'ecryptfs' has been defined in +in order to use encrypted keys to mount an eCryptfs filesystem. More details +about the usage can be found in the file +'Documentation/security/keys-ecryptfs.txt'. |