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SGSN: move cipher application to separate function 

Split out generation and application of GEA gamma into separate function
which can be used for both encryption and decryption.

Change-Id: I442f2ead57e40d9bcd24e7f1b261041371595360
Related: OS#1582
This commit is contained in:
Max 2016-07-11 12:42:12 +02:00 committed by Harald Welte
parent 82040101eb
commit 1de159168c
1 changed files with 42 additions and 41 deletions
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83
openbsc/src/gprs/gprs_llc.c
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@ -347,6 +347,40 @@ static int gprs_llc_tx_xid(struct gprs_llc_lle *lle, struct msgb *msg,
return gprs_llc_tx_u(msg, lle->sapi, command, GPRS_LLC_U_XID, 1);
}
/* encrypt information field + FCS, if needed! */
static int apply_gea(struct gprs_llc_lle *lle, uint16_t crypt_len, uint16_t nu,
uint32_t oc, uint8_t sapi, uint8_t *fcs, uint8_t *data)
{
uint8_t cipher_out[GSM0464_CIPH_MAX_BLOCK];
if (lle->llme->algo == GPRS_ALGO_GEA0)
return -EINVAL;
/* Compute the 'Input' Paraemeter */
uint32_t iv = gprs_cipher_gen_input_ui(lle->llme->iov_ui, sapi,
nu, oc);
/* Compute gamma that we need to XOR with the data */
int r = gprs_cipher_run(cipher_out, crypt_len, lle->llme->algo,
lle->llme->kc, iv,
fcs ? GPRS_CIPH_SGSN2MS : GPRS_CIPH_MS2SGSN);
if (r < 0) {
LOGP(DLLC, LOGL_ERROR, "Error producing %s gamma for UI "
"frame: %d\n", get_value_string(gprs_cipher_names,
lle->llme->algo), r);
return -ENOMSG;
}
if (fcs) {
data += 3;
}
/* XOR the cipher output with the data */
for (r = 0; r < crypt_len; r++)
*(data + r) ^= cipher_out[r];
return 0;
}
/* Transmit a UI frame over the given SAPI:
'encryptable' indicates whether particular message can be encrypted according
to 3GPP TS 24.008 § 4.7.1.2
@ -412,31 +446,13 @@ int gprs_llc_tx_ui(struct msgb *msg, uint8_t sapi, int command,
fcs[1] = (fcs_calc >> 8) & 0xff;
fcs[2] = (fcs_calc >> 16) & 0xff;
/* encrypt information field + FCS, if needed! */
if (lle->llme->algo != GPRS_ALGO_GEA0 && encryptable) {
uint32_t iov_ui = 0; /* FIXME: randomly select for TLLI */
uint16_t crypt_len = (fcs + 3) - (llch + 3);
uint8_t cipher_out[GSM0464_CIPH_MAX_BLOCK];
uint32_t iv;
int rc, i;
uint8_t *kc = lle->llme->kc;
/* Compute the 'Input' Paraemeter */
iv = gprs_cipher_gen_input_ui(iov_ui, sapi, nu, oc);
/* Compute the keystream that we need to XOR with the data */
rc = gprs_cipher_run(cipher_out, crypt_len, lle->llme->algo,
kc, iv, GPRS_CIPH_SGSN2MS);
int rc = apply_gea(lle, fcs - llch, nu, oc, sapi, fcs, llch);
if (rc < 0) {
LOGP(DLLC, LOGL_ERROR, "Error crypting UI frame: %d\n", rc);
msgb_free(msg);
return rc;
}
/* XOR the cipher output with the information field + FCS */
for (i = 0; i < crypt_len; i++)
*(llch + 3 + i) ^= cipher_out[i];
/* Mark frame as encrypted */
ctrl[1] |= 0x02;
}
@ -618,32 +634,17 @@ int gprs_llc_rcvmsg(struct msgb *msg, struct tlv_parsed *tv)
/* decrypt information field + FCS, if needed! */
if (llhp.is_encrypted) {
uint32_t iov_ui = 0; /* FIXME: randomly select for TLLI */
uint16_t crypt_len = llhp.data_len + 3;
uint8_t cipher_out[GSM0464_CIPH_MAX_BLOCK];
uint32_t iv;
uint8_t *kc = lle->llme->kc;
int rc, i;
if (lle->llme->algo == GPRS_ALGO_GEA0) {
if (lle->llme->algo != GPRS_ALGO_GEA0) {
rc = apply_gea(lle, llhp.data_len + 3, llhp.seq_tx,
lle->oc_ui_recv, lle->sapi, NULL,
llhp.data);
if (rc < 0)
return rc;
} else {
LOGP(DLLC, LOGL_NOTICE, "encrypted frame for LLC that "
"has no KC/Algo! Dropping.\n");
return 0;
}
iv = gprs_cipher_gen_input_ui(iov_ui, lle->sapi, llhp.seq_tx,
lle->oc_ui_recv);
rc = gprs_cipher_run(cipher_out, crypt_len, lle->llme->algo,
kc, iv, GPRS_CIPH_MS2SGSN);
if (rc < 0) {
LOGP(DLLC, LOGL_ERROR, "Error decrypting frame: %d\n",
rc);
return rc;
}
/* XOR the cipher output with the information field + FCS */
for (i = 0; i < crypt_len; i++)
*(llhp.data + i) ^= cipher_out[i];
} else {
if (lle->llme->algo != GPRS_ALGO_GEA0 &&
lle->llme->cksn != GSM_KEY_SEQ_INVAL)