From c6bb0eb32d6ef533b61d88bca31fe289c541f749 Mon Sep 17 00:00:00 2001
From: James Prestwood <james.prestwood@linux.intel.com>
Date: Wed, 30 Aug 2017 14:00:21 -0700
Subject: [PATCH] simutil: Added new key/prf functions for EAP-AKA'

This is the core key generation code for the AKA' method which
follows RFC 5448. Two new functions are implemented, one for
deriving CK'/IK' and the other for deriving the encryption keys
using CK'/IK'.
---
 src/simutil.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/simutil.h | 45 +++++++++++++++++++++++
 2 files changed, 143 insertions(+)

diff --git a/src/simutil.c b/src/simutil.c
index 1c496db0..82cb61f3 100644
--- a/src/simutil.c
+++ b/src/simutil.c
@@ -270,6 +270,104 @@ bool eap_aka_get_milenage(const uint8_t *opc, const uint8_t *k,
 	return true;
 }
 
+bool eap_aka_derive_primes(const uint8_t *ck, const uint8_t *ik,
+		const uint8_t *autn, const uint8_t *network, uint16_t net_len,
+		uint8_t *ck_p, uint8_t *ik_p)
+{
+	struct iovec iov[5];
+	struct l_checksum *hmac;
+	uint8_t key[32];
+	uint8_t fc = 0x20;
+	uint16_t l1 = L_CPU_TO_BE16(6);
+	uint16_t name_len = L_CPU_TO_BE16(net_len);
+	uint8_t digest[32];
+
+	memcpy(key, ck, EAP_AKA_CK_LEN);
+	memcpy(key + EAP_AKA_CK_LEN, ik, EAP_AKA_IK_LEN);
+
+	hmac = l_checksum_new_hmac(L_CHECKSUM_SHA256, key, 32);
+	if (!hmac)
+		return false;
+
+	iov[0].iov_base = &fc;
+	iov[0].iov_len = 1;
+	iov[1].iov_base = (void *)network;
+	iov[1].iov_len = net_len;
+	iov[2].iov_base = &name_len;
+	iov[2].iov_len = 2;
+	iov[3].iov_base = (void *)autn;
+	iov[3].iov_len = 6;
+	iov[4].iov_base = &l1;
+	iov[4].iov_len = 2;
+
+	l_checksum_updatev(hmac, iov, 5);
+	l_checksum_get_digest(hmac, digest, 32);
+	l_checksum_free(hmac);
+
+	memcpy(ck_p, digest, EAP_AKA_CK_LEN);
+	memcpy(ik_p, digest + EAP_AKA_CK_LEN, EAP_AKA_IK_LEN);
+
+	return true;
+}
+
+bool eap_aka_prf_prime(const uint8_t *ik_p, const uint8_t *ck_p,
+		const char *identity, uint8_t *k_encr, uint8_t *k_aut,
+		uint8_t *k_re, uint8_t *msk, uint8_t *emsk)
+{
+	struct l_checksum *hmac;
+	uint8_t key[32];
+	struct iovec iov[4];
+	/* digest continues to be reused each iteration */
+	uint8_t digest[32];
+	uint8_t i = 0x01;
+	/* 7 iterations will be 224 bytes, 208 of which will get used */
+	uint8_t out[224];
+	uint8_t *pos = out;
+
+	/* K = (IK'|CK') */
+	memcpy(key, ik_p, EAP_AKA_IK_LEN);
+	memcpy(key + EAP_AKA_IK_LEN, ck_p, EAP_AKA_CK_LEN);
+
+	iov[0].iov_base = digest;
+	/* initial iteration digest is not used */
+	iov[0].iov_len = 0;
+	iov[1].iov_base = (void *)"EAP-AKA'";
+	iov[1].iov_len = strlen("EAP-AKA'");
+	iov[2].iov_base = (void *)identity;
+	iov[2].iov_len = strlen(identity);
+	iov[3].iov_base = &i;
+	iov[3].iov_len = 1;
+
+	/* need 208 bytes for all keys */
+	while (pos < out + 224) {
+		hmac = l_checksum_new_hmac(L_CHECKSUM_SHA256, key, 32);
+		if (!hmac)
+			return false;
+
+		l_checksum_updatev(hmac, iov, 4);
+		l_checksum_get_digest(hmac, digest, 32);
+		l_checksum_free(hmac);
+		memcpy(pos, digest, 32);
+		pos += 32;
+		i++;
+		/* set the digest length so it can be prepended as Tn */
+		iov[0].iov_len = 32;
+	}
+
+	pos = out;
+	memcpy(k_encr, pos, EAP_SIM_K_ENCR_LEN);
+	pos += EAP_SIM_K_ENCR_LEN;
+	memcpy(k_aut, pos, EAP_AKA_PRIME_K_AUT_LEN);
+	pos += EAP_AKA_PRIME_K_AUT_LEN;
+	memcpy(k_re, pos, EAP_AKA_K_RE_LEN);
+	pos += EAP_AKA_K_RE_LEN;
+	memcpy(msk, pos, EAP_SIM_MSK_LEN);
+	pos += EAP_SIM_MSK_LEN;
+	memcpy(emsk, pos, EAP_SIM_EMSK_LEN);
+
+	return true;
+}
+
 void eap_sim_fips_prf(const void *seed, size_t slen, uint8_t *out, size_t olen)
 {
 	uint8_t xkey[64];
diff --git a/src/simutil.h b/src/simutil.h
index bc1a0667..d8a063df 100644
--- a/src/simutil.h
+++ b/src/simutil.h
@@ -28,11 +28,15 @@
 #define EAP_SIM_MK_LEN		20
 #define EAP_SIM_K_ENCR_LEN	16
 #define EAP_SIM_K_AUT_LEN	16
+#define EAP_AKA_PRIME_K_AUT_LEN	32
 #define EAP_SIM_MSK_LEN		64
 #define EAP_SIM_EMSK_LEN	64
 #define EAP_SIM_IV_LEN		16
 #define EAP_SIM_MAC_LEN		16
 #define EAP_SIM_RAND_LEN	16
+#define EAP_AKA_K_RE_LEN	32
+#define EAP_AKA_IK_LEN		16
+#define EAP_AKA_CK_LEN		16
 
 /*
  * Possible pad types for EAP-SIM/EAP-AKA attributes
@@ -151,6 +155,47 @@ bool eap_aka_get_milenage(const uint8_t *opc, const uint8_t *k,
 		const uint8_t *rand, const uint8_t *sqn, const uint8_t *amf,
 		uint8_t *autn, uint8_t *ck, uint8_t *ik, uint8_t *res);
 
+/*
+ * 3GPP TS 33.402
+ * Derivation of CK' and IK' from CK and IK
+ *
+ * FC = 0x20
+ * P0 = access network identity ('network')
+ * L0 = length of P0
+ * P1 = SQN ^ AK = first 6 bytes of AUTN
+ * L1 = length of P1 = 0x0006
+ *
+ * (CK' | IK') = HMAC_SHA256(FC |P0 | L0 | P1 | L1)
+ */
+bool eap_aka_derive_primes(const uint8_t *ck, const uint8_t *ik,
+		const uint8_t *autn, const uint8_t *network, uint16_t net_len,
+		uint8_t *ck_p, uint8_t *ik_p);
+
+/*
+ * RFC 5448, Section 3.4.1
+ *
+ * PRF'(K,S) = T1 | T2 | T3 | T4 | ...
+ *
+ *     where:
+ *     T1 = HMAC-SHA-256 (K, S | 0x01)
+ *     T2 = HMAC-SHA-256 (K, T1 | S | 0x02)
+ *     T3 = HMAC-SHA-256 (K, T2 | S | 0x03)
+ *     T4 = HMAC-SHA-256 (K, T3 | S | 0x04)
+ *     ...
+ *
+ * RFC 5448, Section 3.3
+ *
+ * MK = PRF'(IK'|CK',"EAP-AKA'"|Identity)
+ *      K_encr = MK[0..127]
+ *      K_aut  = MK[128..383]
+ *      K_re   = MK[384..639]
+ *      MSK    = MK[640..1151]
+ *      EMSK   = MK[1152..1663]
+ */
+bool eap_aka_prf_prime(const uint8_t *ik_p, const uint8_t *ck_p,
+		const char *identity, uint8_t *k_encr, uint8_t *k_aut,
+		uint8_t *k_re, uint8_t *msk, uint8_t *emsk);
+
 /*
  * Separate PRNG data into encryption keys. k_encr and k_aut may be NULL in the
  * case of fast re-authentication.