keys: Use accurate logic for eticket keypair read

bdk/utils/util.c

@@ -102,6 +102,27 @@ void exec_cfg(u32 *base, const cfg_op_t *ops, u32 num_ops)
 		base[ops[i].off] = ops[i].val;
 }
 
+u16 crc16_calc(const u8 *buf, u32 len)
+{
+	const u8 *p, *q;
+	u16 crc = 0x55aa;
+
+	static u16 table[16] = {
+		0x0000, 0xCC01, 0xD801, 0x1400, 0xF001, 0x3C00, 0x2800, 0xE401,
+		0xA001, 0x6C00, 0x7800, 0xB401, 0x5000, 0x9C01, 0x8801, 0x4400
+	};
+
+	q = buf + len;
+	for (p = buf; p < q; p++)
+	{
+		u8 oct = *p;
+		crc = (crc >> 4) ^ table[crc & 0xf] ^ table[(oct >> 0) & 0xf];
+		crc = (crc >> 4) ^ table[crc & 0xf] ^ table[(oct >> 4) & 0xf];
+	}
+
+	return crc;
+}
+
 u32 crc32_calc(u32 crc, const u8 *buf, u32 len)
 {
 	const u8 *p, *q;

bdk/utils/util.h

@@ -83,6 +83,7 @@ u8   bit_count(u32 val);
 u32  bit_count_mask(u8 bits);
 
 void exec_cfg(u32 *base, const cfg_op_t *ops, u32 num_ops);
+u16  crc16_calc(const u8 *buf, u32 len);
 u32  crc32_calc(u32 crc, const u8 *buf, u32 len);
 
 u32  get_tmr_us();

source/keys/keys.c

@@ -461,8 +461,23 @@ static bool _derive_titlekeys(key_derivation_ctx_t *keys, titlekey_buffer_t *tit
         return false;
     }
 
+    u32 keypair_generation = 0;
+    const void *eticket_device_key = NULL;
+    const void *eticket_iv = NULL;
+
+    if (cal0->ext_ecc_rsa2048_eticket_key_crc == crc16_calc(cal0->ext_ecc_rsa2048_eticket_key_iv, 0x24E)) {
+        eticket_device_key = cal0->ext_ecc_rsa2048_eticket_key;
+        eticket_iv = cal0->ext_ecc_rsa2048_eticket_key_iv;
+
         // settings sysmodule manually zeroes this out below cal version 9
-    u32 keypair_generation = cal0->version <= 8 ? 0 : cal0->ext_ecc_rsa2048_eticket_key_ver;
+        keypair_generation = cal0->version <= 8 ? 0 : cal0->ext_ecc_rsa2048_eticket_key_ver;
+    } else if (cal0->rsa2048_eticket_key_crc == crc16_calc(cal0->rsa2048_eticket_key_iv, 0x22E)) {
+        eticket_device_key = cal0->rsa2048_eticket_key;
+        eticket_iv = cal0->rsa2048_eticket_key_iv;
+    } else {
+        EPRINTF("Crc16 error reading device key.");
+        return false;
+    }
 
     if (keypair_generation) {
         keypair_generation--;
@@ -478,7 +493,7 @@ static bool _derive_titlekeys(key_derivation_ctx_t *keys, titlekey_buffer_t *tit
     }
 
     se_aes_key_set(6, keys->temp_key, sizeof(keys->temp_key));
-    se_aes_crypt_ctr(6, &rsa_keypair, sizeof(rsa_keypair), cal0->ext_ecc_rsa2048_eticket_key, sizeof(cal0->ext_ecc_rsa2048_eticket_key), cal0->ext_ecc_rsa2048_eticket_key_iv);
+    se_aes_crypt_ctr(6, &rsa_keypair, sizeof(rsa_keypair), eticket_device_key, sizeof(rsa_keypair), eticket_iv);
 
     // Check public exponent is 65537 big endian
     if (_read_be_u32(rsa_keypair.public_exponent, 0) != 65537) {

source/keys/keys.h

@@ -67,9 +67,7 @@ typedef struct {
     u8 private_exponent[RSA_2048_KEY_SIZE];
     u8 modulus[RSA_2048_KEY_SIZE];
     u8 public_exponent[4];
-    u8 reserved[0x14];
+    u8 reserved[0xC];
-    u64 device_id;
-    u8 gmac[0x10];
 } rsa_keypair_t;
 
 typedef struct {

source/storage/nx_emmc_bis.h

@@ -124,8 +124,10 @@ typedef struct _nx_emmc_cal0_t
 	u8   crc16_pad20[0x10];
 	u8   gc_cert[0x400];
 	u8   gc_cert_sha256[0x20];
-	u8   rsa2048_eticket_key[0x220];
+	u8   rsa2048_eticket_key_iv[0x10];
-	u8   crc16_pad21[0x10];
+	u8   rsa2048_eticket_key[0x210];
+	u8   crc16_pad21[0xE];
+	u16  rsa2048_eticket_key_crc;
 	u8   rsa2048_eticket_cert[0x240];
 	u8   crc16_pad22[0x10];
 
@@ -166,7 +168,8 @@ typedef struct _nx_emmc_cal0_t
 	u8   ext_ecc_rsa2048_eticket_key_iv[0x10];
 	u8   ext_ecc_rsa2048_eticket_key[0x230];
 	u32  ext_ecc_rsa2048_eticket_key_ver;
-	u8   crc16_pad38[0xC];
+	u8   crc16_pad38[0xA];
+	u16  ext_ecc_rsa2048_eticket_key_crc;
 	u8   ext_ssl_key[0x130];
 	u8   crc16_pad39[0x10];
 	u8   ext_gc_key[0x130];