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|
/*
* lib/crypto/krb/dk/dk_ccm.c
*
* Copyright 2008-2010 by the Massachusetts Institute of Technology.
* All Rights Reserved.
*
* Export of this software from the United States of America may
* require a specific license from the United States Government.
* It is the responsibility of any person or organization contemplating
* export to obtain such a license before exporting.
*
* WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
* distribute this software and its documentation for any purpose and
* without fee is hereby granted, provided that the above copyright
* notice appear in all copies and that both that copyright notice and
* this permission notice appear in supporting documentation, and that
* the name of M.I.T. not be used in advertising or publicity pertaining
* to distribution of the software without specific, written prior
* permission. Furthermore if you modify this software you must label
* your software as modified software and not distribute it in such a
* fashion that it might be confused with the original M.I.T. software.
* M.I.T. makes no representations about the suitability of
* this software for any purpose. It is provided "as is" without express
* or implied warranty.
*/
#include "k5-int.h"
#include "dk.h"
#include "aead.h"
#ifdef CAMELLIA_CCM
/*
* Implement CCM-mode AEAD as described in section 5.3 and 5.4 of RFC 5116.
* This is the CCM mode as described in NIST SP800-38C, with a 12 byte nonce
* and 16 byte checksum. Multiple buffers of the same type are logically
* concatenated. The underlying enc provider must have a 16-byte block size,
* must have a counter-mode encrypt method, and must have a cbc_mac method.
*
* The IOV should be laid out as follows:
*
* HEADER | SIGN_DATA | DATA | PADDING | TRAILER
*
* SIGN_DATA and PADDING may be absent.
*
* Upon decryption, one can pass in explicit buffers as for encryption, or one
* can pass in STREAM, being the concatenation of HEADER | DATA | TRAILER.
*
* STREAM | SIGN_DATA | DATA
*
* Upon output, DATA will contain a pointer into the STREAM buffer with the
* decrypted payload. SIGN_DATA should be ordered relative to the output DATA
* buffer as it was upon encryption.
*
* For compatibility with RFC 5116, a single key is used both for encryption
* and checksumming. The key derivation function is as follows:
*
* Kc = DK(base-key, usage | 0xCC)
*
* Again as required by the CCM specification, SIGN_DATA is processed before
* DATA for the purpose of checksumming.
*/
#define K5CLENGTH 5 /* 32 bit net byte order integer + one byte seed */
unsigned int
krb5int_dk_ccm_crypto_length(const struct krb5_keytypes *ktp,
krb5_cryptotype type)
{
unsigned int length;
switch (type) {
case KRB5_CRYPTO_TYPE_HEADER:
length = 12; /* RFC 5116 5.3 */
break;
case KRB5_CRYPTO_TYPE_PADDING:
length = 0; /* CTR mode requires no padding */
break;
case KRB5_CRYPTO_TYPE_TRAILER:
case KRB5_CRYPTO_TYPE_CHECKSUM:
length = ktp->enc->block_size;
break;
default:
assert(0 && "invalid cryptotype passed to ccm_crypto_length");
length = ~0;
break;
}
return length;
}
/*
* Encode the length of the additional data according to NIST SP800-38C section
* A.2.2. The size of the encoding will be 0, 2, 6, or 10 bytes depending on
* the length value.
*/
static krb5_error_code
encode_a_len(krb5_data *a, krb5_ui_8 adata_len)
{
size_t len;
unsigned char *p;
if (adata_len > (1LL << 32))
len = 10;
else if (adata_len > (1LL << 16) - (1LL << 8))
len = 6;
else if (adata_len)
len = 2;
else
len = 0;
if (a->length < len)
return KRB5_BAD_MSIZE;
p = (unsigned char *)a->data;
switch (len) {
case 2:
/* Two raw bytes; first byte will not be 0xFF. */
p[0] = (adata_len >> 8) & 0xFF;
p[1] = (adata_len ) & 0xFF;
break;
case 6:
/* FF FE followed by four bytes. */
p[0] = 0xFF;
p[1] = 0xFE;
p[2] = (adata_len >> 24) & 0xFF;
p[3] = (adata_len >> 16) & 0xFF;
p[4] = (adata_len >> 8 ) & 0xFF;
p[5] = (adata_len ) & 0xFF;
break;
case 10:
/* FF FF followed by eight bytes. */
p[0] = 0xFF;
p[1] = 0xFF;
p[2] = (adata_len >> 56) & 0xFF;
p[3] = (adata_len >> 48) & 0xFF;
p[4] = (adata_len >> 40) & 0xFF;
p[5] = (adata_len >> 32) & 0xFF;
p[6] = (adata_len >> 24) & 0xFF;
p[7] = (adata_len >> 16) & 0xFF;
p[8] = (adata_len >> 8 ) & 0xFF;
p[9] = (adata_len ) & 0xFF;
break;
}
a->length = len;
return 0;
}
/*
* Encode the first 16-byte block of CBC-MAC input according to NIST SP800-38C
* section A.2.1. n (the nonce length) is given by nonce->length.
*/
static krb5_error_code
format_B0(krb5_data *B0, /* B0 */
krb5_data *nonce, /* N */
size_t trailer_len, /* t */
krb5_ui_8 adata_len, /* a */
krb5_ui_8 payload_len) /* Q */
{
unsigned char flags;
unsigned char *p;
krb5_octet q, i = 0;
if (B0->length != 16)
return KRB5_BAD_MSIZE;
/* Section A.1: Length Requirements */
/* t is an element of {4, 6, 8, 10, 12, 14, 16}. */
if (trailer_len % 2 ||
(trailer_len < 4 || trailer_len > 16))
return KRB5_BAD_MSIZE;
/* n is an element of {7, 8, 9, 10, 11, 12, 13}. */
if (nonce->length < 7 || nonce->length > 13)
return KRB5_BAD_MSIZE;
q = 15 - nonce->length;
/* P consists of fewer than 2^(8q) octets. */
if (payload_len >= (1UL << (8 * q)))
return KRB5_BAD_MSIZE;
/* Encode the flags octet. */
flags = q - 1;
flags |= (((trailer_len - 2) / 2) << 3);
if (adata_len != 0)
flags |= (1 << 6);
p = (unsigned char *)B0->data;
p[i++] = flags;
/* Next comes the nonce (n bytes). */
memcpy(&p[i], nonce->data, nonce->length);
i += nonce->length;
/* The final q bytes are the payload length. */
for (; i < B0->length; i++) {
register krb5_octet s;
s = (q - (i - nonce->length)) * 8;
p[i] = (payload_len >> s) & 0xFF;
}
return 0;
}
/*
* Encode the initial counter block according to NIST SP800-38C section A.3.
* The counter value may be chained across krb5_k_encrypt invocations via the
* cipher_state parameter; otherwise it begins at 0.
*/
static krb5_error_code
format_Ctr0(krb5_data *counter, const krb5_data *nonce, const krb5_data *state,
unsigned int n)
{
krb5_octet q; /* counter length */
assert(n >= 7 && n <= 13);
/* First byte is q-1 in the lowest three bits. */
q = 15 - n;
counter->data[0] = q - 1;
/* Next comes the nonce (n bytes). */
memcpy(&counter->data[1], nonce->data, n);
/* Finally, the counter value. */
if (state != NULL)
memcpy(&counter->data[1 + n], state->data, q);
else
memset(&counter->data[1 + n], 0, q);
return 0;
}
/* Return true if the payload length is valid given the nonce length n. */
static krb5_boolean
valid_payload_length_p(const struct krb5_keytypes *ktp, unsigned int n,
unsigned int payload_len)
{
unsigned int block_size = ktp->enc->block_size;
unsigned int nblocks, maxblocks;
krb5_octet q;
assert(n >= 7 && n <= 13);
q = 15 - n;
maxblocks = (1U << (8 * q)) - 1 /* tag */;
nblocks = (payload_len + block_size - 1) / block_size;
return (nblocks <= maxblocks);
}
/* Encrypt and authenticate data according to NIST SP800-38C section 6.1. */
static krb5_error_code
ccm_encrypt(const struct krb5_keytypes *ktp, krb5_key kc,
const krb5_data *state, krb5_crypto_iov *data, size_t num_data)
{
krb5_error_code ret;
krb5_crypto_iov *header, *trailer, *sign_data = NULL, cksum;
size_t i, num_sign_data = 0;
unsigned int header_len;
unsigned int trailer_len;
size_t payload_len = 0;
size_t adata_len = 0;
char adata_len_buf[6];
unsigned char B0[16], Ctr[16];
krb5_data counter = make_data(Ctr, sizeof(Ctr));
header_len = ktp->crypto_length(ktp, KRB5_CRYPTO_TYPE_HEADER);
header = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_HEADER);
if (header == NULL || header->data.length < header_len) {
ret = KRB5_BAD_MSIZE;
goto cleanup;
}
trailer_len = ktp->crypto_length(ktp, KRB5_CRYPTO_TYPE_TRAILER);
trailer = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_TRAILER);
if (trailer == NULL || trailer->data.length < trailer_len) {
ret = KRB5_BAD_MSIZE;
goto cleanup;
}
for (i = 0; i < num_data; i++) {
krb5_crypto_iov *iov = &data[i];
switch (iov->flags) {
case KRB5_CRYPTO_TYPE_DATA:
payload_len += iov->data.length;
break;
case KRB5_CRYPTO_TYPE_SIGN_ONLY:
adata_len += iov->data.length;
break;
case KRB5_CRYPTO_TYPE_PADDING:
iov->data.length = 0;
break;
default:
break;
}
}
if (!valid_payload_length_p(ktp, header_len, payload_len)) {
ret = KRB5_BAD_MSIZE;
goto cleanup;
}
header->data.length = header_len;
trailer->data.length = trailer_len;
/* Choose a random nonce. */
ret = krb5_c_random_make_octets(NULL, &header->data);
if (ret != 0)
goto cleanup;
/* Encode the first counter block. */
ret = format_Ctr0(&counter, &header->data, state, header_len);
if (ret != 0)
goto cleanup;
/* Create a list of CBC-MAC input blocks. */
sign_data = k5alloc((num_data + 1) * sizeof(krb5_crypto_iov), &ret);
if (sign_data == NULL)
goto cleanup;
/* Format the initial control/nonce block. */
sign_data[0].flags = KRB5_CRYPTO_TYPE_HEADER;
sign_data[0].data = make_data(B0, sizeof(B0));
ret = format_B0(&sign_data[0].data, &header->data, trailer_len,
(krb5_ui_8)adata_len, (krb5_ui_8)payload_len);
if (ret != 0)
goto cleanup;
/* Format the length of associated data. */
sign_data[1].flags = KRB5_CRYPTO_TYPE_SIGN_ONLY;
sign_data[1].data = make_data(adata_len_buf, sizeof(adata_len_buf));
ret = encode_a_len(&sign_data[1].data, (krb5_ui_8)adata_len);
if (ret != 0)
goto cleanup;
num_sign_data = 2;
/* Reorder input IOV so SIGN_ONLY data is before DATA. */
for (i = 0; i < num_data; i++) {
if (data[i].flags == KRB5_CRYPTO_TYPE_SIGN_ONLY)
sign_data[num_sign_data++] = data[i];
}
for (i = 0; i < num_data; i++) {
if (data[i].flags == KRB5_CRYPTO_TYPE_DATA)
sign_data[num_sign_data++] = data[i];
}
assert(ktp->enc->encrypt != NULL);
assert(ktp->enc->cbc_mac != NULL);
/* Make checksum and place in trailer. */
ret = ktp->enc->cbc_mac(kc, sign_data, num_sign_data, NULL,
&trailer->data);
if (ret != 0)
goto cleanup;
/* Encrypt checksum in trailer using the first counter block. */
cksum.flags = KRB5_CRYPTO_TYPE_DATA;
cksum.data = trailer->data;
ret = ktp->enc->encrypt(kc, &counter, &cksum, 1);
if (ret != 0)
goto cleanup;
/* Encrypt everything but B0 (header) in subsequent counter blocks. */
ret = ktp->enc->encrypt(kc, &counter, data, num_data);
if (ret != 0)
goto cleanup;
/* Store the counter value as cipher state. Subsequent encryptions will
* generate a fresh nonce. */
if (state != NULL)
memcpy(state->data, counter.data + 1 + header_len, 15 - header_len);
cleanup:
free(sign_data);
return ret;
}
/* Derive an encryption key based on usage and CCM-encrypt data. */
krb5_error_code
krb5int_dk_ccm_encrypt(const struct krb5_keytypes *ktp, krb5_key key,
krb5_keyusage usage, const krb5_data *state,
krb5_crypto_iov *data, size_t num_data)
{
unsigned char constantdata[K5CLENGTH];
krb5_error_code ret;
krb5_key kc;
krb5_data d1;
d1.data = (char *)constantdata;
d1.length = K5CLENGTH;
d1.data[0] = (usage >> 24) & 0xFF;
d1.data[1] = (usage >> 16) & 0xFF;
d1.data[2] = (usage >> 8 ) & 0xFF;
d1.data[3] = (usage ) & 0xFF;
d1.data[4] = 0xCC;
ret = krb5int_derive_key(ktp->enc, key, &kc, &d1, DERIVE_SP800_108_CMAC);
if (ret != 0)
return ret;
ret = ccm_encrypt(ktp, kc, state, data, num_data);
krb5_k_free_key(NULL, kc);
return ret;
}
/* Decrypt and verify data according to NIST SP800-38C section 6.2. */
static krb5_error_code
ccm_decrypt(const struct krb5_keytypes *ktp, krb5_key kc,
const krb5_data *state, krb5_crypto_iov *data, size_t num_data)
{
krb5_error_code ret;
krb5_crypto_iov *header, *trailer, *sign_data = NULL, got_cksum;
size_t i, num_sign_data = 0;
unsigned int header_len;
unsigned int trailer_len;
size_t adata_len = 0;
size_t payload_len = 0;
char adata_len_buf[6];
unsigned char B0[16], Ctr[16];
krb5_data made_cksum = empty_data();
krb5_data counter = make_data(Ctr, sizeof(Ctr));
header_len = ktp->crypto_length(ktp, KRB5_CRYPTO_TYPE_HEADER);
header = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_HEADER);
if (header == NULL || header->data.length != header_len) {
ret = KRB5_BAD_MSIZE;
goto cleanup;
}
trailer_len = ktp->crypto_length(ktp, KRB5_CRYPTO_TYPE_TRAILER);
trailer = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_TRAILER);
if (trailer == NULL || trailer->data.length != trailer_len) {
ret = KRB5_BAD_MSIZE;
goto cleanup;
}
for (i = 0; i < num_data; i++) {
krb5_crypto_iov *iov = &data[i];
switch (iov->flags) {
case KRB5_CRYPTO_TYPE_DATA:
payload_len += iov->data.length;
break;
case KRB5_CRYPTO_TYPE_SIGN_ONLY:
adata_len += iov->data.length;
break;
case KRB5_CRYPTO_TYPE_PADDING:
if (iov->data.length != 0) {
ret = KRB5_BAD_MSIZE;
goto cleanup;
}
break;
default:
break;
}
}
if (!valid_payload_length_p(ktp, header_len, payload_len)) {
ret = KRB5_BAD_MSIZE;
goto cleanup;
}
/* Encode the first counter block. */
ret = format_Ctr0(&counter, &header->data, state, header_len);
if (ret != 0)
goto cleanup;
/* Create a list of CBC-MAC input blocks. */
sign_data = k5alloc((num_data + 1) * sizeof(krb5_crypto_iov), &ret);
if (sign_data == NULL)
goto cleanup;
/* Format the initial control/nonce block. */
sign_data[0].flags = KRB5_CRYPTO_TYPE_HEADER;
sign_data[0].data = make_data(B0, sizeof(B0));
ret = format_B0(&sign_data[0].data, &header->data, trailer_len,
(krb5_ui_8)adata_len, (krb5_ui_8)payload_len);
if (ret != 0)
goto cleanup;
/* Format the length of associated data. */
sign_data[1].flags = KRB5_CRYPTO_TYPE_SIGN_ONLY;
sign_data[1].data = make_data(adata_len_buf, sizeof(adata_len_buf));
ret = encode_a_len(&sign_data[1].data, (krb5_ui_8)adata_len);
if (ret != 0)
goto cleanup;
num_sign_data = 2;
assert(ktp->enc->decrypt != NULL);
assert(ktp->enc->cbc_mac != NULL);
made_cksum.data = k5alloc(trailer_len, &ret);
if (made_cksum.data == NULL)
goto cleanup;
made_cksum.length = trailer_len;
/* Decrypt checksum from trailer using the first counter block. */
got_cksum.flags = KRB5_CRYPTO_TYPE_DATA;
got_cksum.data = trailer->data;
ret = ktp->enc->decrypt(kc, &counter, &got_cksum, 1);
if (ret != 0)
goto cleanup;
/* Decrypt everything but B0 (header) in subsequent counter blocks. */
ret = ktp->enc->decrypt(kc, &counter, data, num_data);
if (ret != 0)
goto cleanup;
/* Reorder input IOV so SIGN_ONLY data is before DATA */
for (i = 0; i < num_data; i++) {
if (data[i].flags == KRB5_CRYPTO_TYPE_SIGN_ONLY)
sign_data[num_sign_data++] = data[i];
}
for (i = 0; i < num_data; i++) {
if (data[i].flags == KRB5_CRYPTO_TYPE_DATA)
sign_data[num_sign_data++] = data[i];
}
/* Calculate CBC-MAC for comparison (including B0). */
ret = ktp->enc->cbc_mac(kc, sign_data, num_sign_data, NULL, &made_cksum);
if (ret != 0)
goto cleanup;
if (made_cksum.length != trailer->data.length ||
memcmp(made_cksum.data, trailer->data.data,
trailer->data.length) != 0) {
ret = KRB5KRB_AP_ERR_BAD_INTEGRITY;
goto cleanup;
}
/* Store the counter value as cipher state. Subsequent encryptions will
* generate a fresh nonce. */
if (state != NULL)
memcpy(state->data, counter.data + 1 + header_len, 15 - header_len);
cleanup:
free(made_cksum.data);
free(sign_data);
return ret;
}
/* Derive an encryption key based on usage and CCM-decrypt data. */
krb5_error_code
krb5int_dk_ccm_decrypt(const struct krb5_keytypes *ktp, krb5_key key,
krb5_keyusage usage, const krb5_data *state,
krb5_crypto_iov *data, size_t num_data)
{
unsigned char constantdata[K5CLENGTH];
krb5_error_code ret;
krb5_key kc;
krb5_data d1;
d1.data = (char *)constantdata;
d1.length = K5CLENGTH;
d1.data[0] = (usage >> 24) & 0xFF;
d1.data[1] = (usage >> 16) & 0xFF;
d1.data[2] = (usage >> 8 ) & 0xFF;
d1.data[3] = (usage ) & 0xFF;
d1.data[4] = 0xCC;
ret = krb5int_derive_key(ktp->enc, key, &kc, &d1, DERIVE_SP800_108_CMAC);
if (ret != 0)
return ret;
ret = ccm_decrypt(ktp, kc, state, data, num_data);
krb5_k_free_key(NULL, kc);
return ret;
}
krb5_error_code
krb5int_dk_ccm_init_state(const struct krb5_keytypes *ktp,
const krb5_keyblock *key, krb5_keyusage usage,
krb5_data *out_state)
{
unsigned int header_len;
/* The cipher state is the q-byte block counter value. */
header_len = ktp->crypto_length(ktp, KRB5_CRYPTO_TYPE_HEADER);
return alloc_data(out_state, 15 - header_len);
}
void
krb5int_dk_ccm_free_state(const struct krb5_keytypes *ktp,
krb5_data *state)
{
free(state->data);
state->data = NULL;
state->length = 0;
}
#endif /* CAMELLIA_CCM */
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