[RFC][PATCH v3 3/6] encrypted-keys: add key format support

Roberto Sassu
2011-01-24T16:45:32Z

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This patch introduces a new parameter, called 'format', that defines the
format of data stored by encrypted keys. The 'default' format identifies
encrypted keys containing only the symmetric key, while other formats can
be defined to support additional information. The 'format' parameter is
written in the datablob produced by commands 'keyctl print' or
'keyctl pipe' and is integrity protected by the HMAC.

Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Acked-by: Gianluca Ramunno <ramunno@polito.it>
Acked-by: Mimi Zohar <zohar@us.ibm.com>
---
Documentation/keys-trusted-encrypted.txt | 48 +++++++----
include/keys/encrypted-type.h | 13 +++-
security/keys/encrypted.c | 141 +++++++++++++++++++++---------
3 files changed, 142 insertions(+), 60 deletions(-)

diff --git a/Documentation/keys-trusted-encrypted.txt b/Documentation/keys-trusted-encrypted.txt
index 8fb79bc..0afcb50 100644
--- a/Documentation/keys-trusted-encrypted.txt
+++ b/Documentation/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'
+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 +149,9 @@ Load an encrypted key "evm" from saved blob:
831684262

$ keyctl print 831684262
- trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382dbbc55
- be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e024717c64
- 5972dcb82ab2dde83376d82b2e3c09ffc
-
+ default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
+ 82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
+ 24717c64 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.
+Other uses for trusted and encrypted keys, such as for disk and file encryption
+are anticipated.
diff --git a/include/keys/encrypted-type.h b/include/keys/encrypted-type.h
index 9585501..1d45413 100644
--- a/include/keys/encrypted-type.h
+++ b/include/keys/encrypted-type.h
@@ -1,6 +1,11 @@
/*
* Copyright (C) 2010 IBM Corporation
- * Author: Mimi Zohar <zohar@us.ibm.com>
+ * Copyright (C) 2010 Politecnico di Torino, Italy
+ * TORSEC group -- http://security.polito.it
+ *
+ * Authors:
+ * Mimi Zohar <zohar@us.ibm.com>
+ * Roberto Sassu <roberto.sassu@polito.it>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@@ -15,13 +20,17 @@

struct encrypted_key_payload {
struct rcu_head rcu;
+ char *format; /* datablob: format */
char *master_desc; /* datablob: master key name */
char *datalen; /* datablob: decrypted key length */
u8 *iv; /* datablob: iv */
u8 *encrypted_data; /* datablob: encrypted data */
unsigned short datablob_len; /* length of datablob */
unsigned short decrypted_datalen; /* decrypted data length */
- u8 decrypted_data[0]; /* decrypted data + datablob + hmac */
+ unsigned short payload_datalen; /* payload data length */
+ unsigned short encrypted_key_format; /* encrypted key format */
+ u8 *decrypted_data; /* decrypted data */
+ u8 payload_data[0]; /* payload data + datablob + hmac */
};

extern struct key_type key_type_encrypted;
diff --git a/security/keys/encrypted.c b/security/keys/encrypted.c
index 322e979..59f719e 100644
--- a/security/keys/encrypted.c
+++ b/security/keys/encrypted.c
@@ -1,8 +1,11 @@
/*
* Copyright (C) 2010 IBM Corporation
+ * Copyright (C) 2010 Politecnico di Torino, Italy
+ * TORSEC group -- http://security.polito.it
*
- * Author:
+ * Authors:
* Mimi Zohar <zohar@us.ibm.com>
+ * Roberto Sassu <roberto.sassu@polito.it>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@@ -37,6 +40,7 @@ static const char KEY_USER_PREFIX[] = "user:";
static const char hash_alg[] = "sha256";
static const char hmac_alg[] = "hmac(sha256)";
static const char blkcipher_alg[] = "cbc(aes)";
+static const char key_format_default[] = "default";
static unsigned int ivsize;
static int blksize;

@@ -58,6 +62,15 @@ enum {
Opt_err = -1, Opt_new, Opt_load, Opt_update
};

+enum {
+ Opt_error = -1, Opt_default
+};
+
+static const match_table_t key_format_tokens = {
+ {Opt_default, "default"},
+ {Opt_error, NULL}
+};
+
static const match_table_t key_tokens = {
{Opt_new, "new"},
{Opt_load, "load"},
@@ -118,8 +131,9 @@ out:
* datablob_parse - parse the keyctl data
*
* datablob format:
- * new <master-key name> <decrypted data length>
- * load <master-key name> <decrypted data length> <encrypted iv + data>
+ * new [<format>] <master-key name> <decrypted data length>
+ * load [<format>] <master-key name> <decrypted data length>
+ * <encrypted iv + data>
* update <new-master-key name>
*
* Tokenizes a copy of the keyctl data, returning a pointer to each token,
@@ -127,13 +141,15 @@ out:
*
* On success returns 0, otherwise -EINVAL.
*/
-static int datablob_parse(char *datablob, char **master_desc,
- char **decrypted_datalen, char **hex_encoded_iv)
+static int datablob_parse(char *datablob, const char **format,
+ char **master_desc, char **decrypted_datalen,
+ char **hex_encoded_iv)
{
substring_t args[MAX_OPT_ARGS];
int ret = -EINVAL;
int key_cmd;
- char *keyword;
+ int key_format;
+ char *p, *keyword;

keyword = strsep(&datablob, " \t");
if (!keyword) {
@@ -142,7 +158,24 @@ static int datablob_parse(char *datablob, char **master_desc,
}
key_cmd = match_token(keyword, key_tokens, args);

- *master_desc = strsep(&datablob, " \t");
+ /* Get optional format: default */
+ p = strsep(&datablob, " \t");
+ if (!p) {
+ pr_err("encrypted_key: insufficient parameters specified\n");
+ return ret;
+ }
+
+ key_format = match_token(p, key_format_tokens, args);
+ switch (key_format) {
+ case Opt_default:
+ *format = p;
+ *master_desc = strsep(&datablob, " \t");
+ break;
+ case Opt_error:
+ *master_desc = p;
+ break;
+ }
+
if (!*master_desc) {
pr_err("encrypted_key: master key parameter is missing\n");
goto out;
@@ -219,8 +252,8 @@ static char *datablob_format(struct encrypted_key_payload *epayload,
ascii_buf[asciiblob_len] = '\0';

/* copy datablob master_desc and datalen strings */
- len = sprintf(ascii_buf, "%s %s ", epayload->master_desc,
- epayload->datalen);
+ len = sprintf(ascii_buf, "%s %s %s ", epayload->format,
+ epayload->master_desc, epayload->datalen);

/* convert the hex encoded iv, encrypted-data and HMAC to ascii */
bufp = &ascii_buf[len];
@@ -461,9 +494,9 @@ static int datablob_hmac_append(struct encrypted_key_payload *epayload,
if (ret < 0)
goto out;

- digest = epayload->master_desc + epayload->datablob_len;
+ digest = epayload->format + epayload->datablob_len;
ret = calc_hmac(digest, derived_key, sizeof derived_key,
- epayload->master_desc, epayload->datablob_len);
+ epayload->format, epayload->datablob_len);
if (!ret)
dump_hmac(NULL, digest, HASH_SIZE);
out:
@@ -472,26 +505,35 @@ out:

/* verify HMAC before decrypting encrypted key */
static int datablob_hmac_verify(struct encrypted_key_payload *epayload,
- const u8 *master_key, size_t master_keylen)
+ const u8 *format, const u8 *master_key,
+ size_t master_keylen)
{
u8 derived_key[HASH_SIZE];
u8 digest[HASH_SIZE];
int ret;
+ char *p;
+ unsigned short len;

ret = get_derived_key(derived_key, AUTH_KEY, master_key, master_keylen);
if (ret < 0)
goto out;

- ret = calc_hmac(digest, derived_key, sizeof derived_key,
- epayload->master_desc, epayload->datablob_len);
+ len = epayload->datablob_len;
+ if (!format) {
+ p = epayload->master_desc;
+ len -= strlen(epayload->format) + 1;
+ } else
+ p = epayload->format;
+
+ ret = calc_hmac(digest, derived_key, sizeof derived_key, p, len);
if (ret < 0)
goto out;
- ret = memcmp(digest, epayload->master_desc + epayload->datablob_len,
+ ret = memcmp(digest, epayload->format + epayload->datablob_len,
sizeof digest);
if (ret) {
ret = -EINVAL;
dump_hmac("datablob",
- epayload->master_desc + epayload->datablob_len,
+ epayload->format + epayload->datablob_len,
HASH_SIZE);
dump_hmac("calc", digest, HASH_SIZE);
}
@@ -536,13 +578,16 @@ out:

/* Allocate memory for decrypted key and datablob. */
static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
+ const char *format,
const char *master_desc,
const char *datalen)
{
struct encrypted_key_payload *epayload = NULL;
unsigned short datablob_len;
unsigned short decrypted_datalen;
+ unsigned short payload_datalen;
unsigned int encrypted_datalen;
+ unsigned int format_len;
long dlen;
int ret;

@@ -550,29 +595,32 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
if (ret < 0 || dlen < MIN_DATA_SIZE || dlen > MAX_DATA_SIZE)
return ERR_PTR(-EINVAL);

+ format_len = (!format) ? strlen(key_format_default) : strlen(format);
decrypted_datalen = dlen;
+ payload_datalen = decrypted_datalen;
encrypted_datalen = roundup(decrypted_datalen, blksize);

- datablob_len = strlen(master_desc) + 1 + strlen(datalen) + 1
- + ivsize + 1 + encrypted_datalen;
+ datablob_len = format_len + 1 + strlen(master_desc) + 1
+ + strlen(datalen) + 1 + ivsize + 1 + encrypted_datalen;

- ret = key_payload_reserve(key, decrypted_datalen + datablob_len
+ ret = key_payload_reserve(key, payload_datalen + datablob_len
+ HASH_SIZE + 1);
if (ret < 0)
return ERR_PTR(ret);

- epayload = kzalloc(sizeof(*epayload) + decrypted_datalen +
+ epayload = kzalloc(sizeof(*epayload) + payload_datalen +
datablob_len + HASH_SIZE + 1, GFP_KERNEL);
if (!epayload)
return ERR_PTR(-ENOMEM);

+ epayload->payload_datalen = payload_datalen;
epayload->decrypted_datalen = decrypted_datalen;
epayload->datablob_len = datablob_len;
return epayload;
}

static int encrypted_key_decrypt(struct encrypted_key_payload *epayload,
- const char *hex_encoded_iv)
+ const char *format, const char *hex_encoded_iv)
{
struct key *mkey;
u8 derived_key[HASH_SIZE];
@@ -593,14 +641,14 @@ static int encrypted_key_decrypt(struct encrypted_key_payload *epayload,
hex2bin(epayload->iv, hex_encoded_iv, ivsize);
hex2bin(epayload->encrypted_data, hex_encoded_data, encrypted_datalen);

- hmac = epayload->master_desc + epayload->datablob_len;
+ hmac = epayload->format + epayload->datablob_len;
hex2bin(hmac, hex_encoded_data + (encrypted_datalen * 2), HASH_SIZE);

mkey = request_master_key(epayload, &master_key, &master_keylen);
if (IS_ERR(mkey))
return PTR_ERR(mkey);

- ret = datablob_hmac_verify(epayload, master_key, master_keylen);
+ ret = datablob_hmac_verify(epayload, format, master_key, master_keylen);
if (ret < 0) {
pr_err("encrypted_key: bad hmac (%d)\n", ret);
goto out;
@@ -620,14 +668,23 @@ out:
}

static void __ekey_init(struct encrypted_key_payload *epayload,
- const char *master_desc, const char *datalen)
+ const char *format, const char *master_desc,
+ const char *datalen)
{
- epayload->master_desc = epayload->decrypted_data
- + epayload->decrypted_datalen;
+ unsigned int format_len;
+
+ format_len = (!format) ? strlen(key_format_default) : strlen(format);
+ epayload->format = epayload->payload_data + epayload->payload_datalen;
+ epayload->master_desc = epayload->format + format_len + 1;
epayload->datalen = epayload->master_desc + strlen(master_desc) + 1;
epayload->iv = epayload->datalen + strlen(datalen) + 1;
epayload->encrypted_data = epayload->iv + ivsize + 1;
+ epayload->decrypted_data = epayload->payload_data;

+ if (!format)
+ memcpy(epayload->format, key_format_default, format_len);
+ else
+ memcpy(epayload->format, format, format_len);
memcpy(epayload->master_desc, master_desc, strlen(master_desc));
memcpy(epayload->datalen, datalen, strlen(datalen));
}
@@ -639,19 +696,19 @@ static void __ekey_init(struct encrypted_key_payload *epayload,
* itself. For an old key, decrypt the hex encoded data.
*/
static int encrypted_init(struct encrypted_key_payload *epayload,
- const char *master_desc, const char *datalen,
- const char *hex_encoded_iv)
+ const char *format, const char *master_desc,
+ const char *datalen, const char *hex_encoded_iv)
{
int ret = 0;

- __ekey_init(epayload, master_desc, datalen);
+ __ekey_init(epayload, format, master_desc, datalen);
if (!hex_encoded_iv) {
get_random_bytes(epayload->iv, ivsize);

get_random_bytes(epayload->decrypted_data,
epayload->decrypted_datalen);
} else
- ret = encrypted_key_decrypt(epayload, hex_encoded_iv);
+ ret = encrypted_key_decrypt(epayload, format, hex_encoded_iv);
return ret;
}

@@ -668,6 +725,7 @@ static int encrypted_instantiate(struct key *key, const void *data,
{
struct encrypted_key_payload *epayload = NULL;
char *datablob = NULL;
+ const char *format = NULL;
char *master_desc = NULL;
char *decrypted_datalen = NULL;
char *hex_encoded_iv = NULL;
@@ -681,17 +739,18 @@ static int encrypted_instantiate(struct key *key, const void *data,
return -ENOMEM;
datablob[datalen] = 0;
memcpy(datablob, data, datalen);
- ret = datablob_parse(datablob, &master_desc, &decrypted_datalen,
- &hex_encoded_iv);
+ ret = datablob_parse(datablob, &format, &master_desc,
+ &decrypted_datalen, &hex_encoded_iv);
if (ret < 0)
goto out;

- epayload = encrypted_key_alloc(key, master_desc, decrypted_datalen);
+ epayload = encrypted_key_alloc(key, format, master_desc,
+ decrypted_datalen);
if (IS_ERR(epayload)) {
ret = PTR_ERR(epayload);
goto out;
}
- ret = encrypted_init(epayload, master_desc, decrypted_datalen,
+ ret = encrypted_init(epayload, format, master_desc, decrypted_datalen,
hex_encoded_iv);
if (ret < 0) {
kfree(epayload);
@@ -728,6 +787,7 @@ static int encrypted_update(struct key *key, const void *data, size_t datalen)
struct encrypted_key_payload *new_epayload;
char *buf;
char *new_master_desc = NULL;
+ const char *format = NULL;
int ret = 0;

if (datalen <= 0 || datalen > 32767 || !data)
@@ -739,7 +799,7 @@ static int encrypted_update(struct key *key, const void *data, size_t datalen)

buf[datalen] = 0;
memcpy(buf, data, datalen);
- ret = datablob_parse(buf, &new_master_desc, NULL, NULL);
+ ret = datablob_parse(buf, &format, &new_master_desc, NULL, NULL);
if (ret < 0)
goto out;

@@ -747,18 +807,19 @@ static int encrypted_update(struct key *key, const void *data, size_t datalen)
if (ret < 0)
goto out;

- new_epayload = encrypted_key_alloc(key, new_master_desc,
- epayload->datalen);
+ new_epayload = encrypted_key_alloc(key, epayload->format,
+ new_master_desc, epayload->datalen);
if (IS_ERR(new_epayload)) {
ret = PTR_ERR(new_epayload);
goto out;
}

- __ekey_init(new_epayload, new_master_desc, epayload->datalen);
+ __ekey_init(new_epayload, epayload->format, new_master_desc,
+ epayload->datalen);

memcpy(new_epayload->iv, epayload->iv, ivsize);
- memcpy(new_epayload->decrypted_data, epayload->decrypted_data,
- epayload->decrypted_datalen);
+ memcpy(new_epayload->payload_data, epayload->payload_data,
+ epayload->payload_datalen);

rcu_assign_pointer(key->payload.data, new_epayload);
call_rcu(&epayload->rcu, encrypted_rcu_free);
--
1.7.3.4

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