Implement Nintendo's non-standard AES-GCM.

exosphere/gcm.c

@@ -0,0 +1,167 @@
+#include <stdint.h>
+
+#include "utils.h"
+#include "gcm.h"
+
+#include "sealedkeys.h"
+#include "se.h"
+
+/* Shifts right a little endian 128-bit value. */
+void shr_128(uint64_t *val) {
+    val[0] >>= 1;
+    val[0] |= (val[1] & 1) << 63;
+    val[1] >>= 1;
+}
+
+/* Shifts left a little endian 128-bit value. */
+void shl_128(uint64_t *val) {
+    val[1] <<= 1;
+    val[1] |= (val[0] & (1ULL << 63)) >> 63;
+    val[0] <<= 1;
+}
+
+
+/* Multiplies two 128-bit numbers X,Y in the GF(128) Galois Field. */
+void gf128_mul(uint8_t *dst, const uint8_t *x, const uint8_t *y) {
+    uint8_t x_work[0x10];
+    uint8_t y_work[0x10];
+    uint8_t dst_work[0x10];
+    
+    uint64_t *p_x = (uint64_t *)(&x_work[0]);
+    uint64_t *p_y = (uint64_t *)(&y_work[0]);
+    uint64_t *p_dst = (uint64_t *)(&dst_work[0]);
+    
+    /* Initialize buffers. */
+    for (unsigned int i = 0; i < 0x10; i++) {
+        x_work[i] = x[0xF-i];
+        y_work[i] = y[0xF-i];
+        dst_work[i] = 0;
+    }
+    
+    /* Perform operation for each bit in y. */
+    for (unsigned int round = 0; round < 0x80; round++) {
+        p_dst[0] ^= p_x[0] * ((y_work[0xF] & 0x80) >> 7);
+        p_dst[1] ^= p_x[1] * ((y_work[0xF] & 0x80) >> 7);
+        shl_128(p_y);
+        uint8_t xor = 0xE1 * (x_work[0] & 1);
+        shr_128(p_x);
+        x_work[0xF] ^= xor;
+    }
+    
+    for (unsigned int i = 0; i < 0x10; i++) {
+        dst[i] = dst_work[0xF-i];
+    }
+}
+
+
+
+/* Performs an AES-GCM GHASH operation over the data into dst. */
+void ghash(void *dst, const void *data, size_t data_size, const void *j_block, int encrypt) {
+    uint8_t x[0x10];
+    uint8_t h[0x10];
+    
+    uint64_t *p_x = (uint64_t *)(&x[0]);
+    uint64_t *p_data = (uint64_t *)data;
+    
+    for (unsigned int i = 0; i < 0x10; i++) {
+        x[i] = 0;
+    }
+    
+    /* H = aes_ecb_encrypt(zeroes) */
+    se_aes_ecb_encrypt_block(KEYSLOT_SWITCH_TEMPKEY, h, 0x10, x, 0x10);
+
+    size_t total_size = data_size;
+    
+    while (data_size >= 0x10) {
+        /* X = (X ^ current_block) * H */
+        p_x[0] ^= p_data[0];
+        p_x[1] ^= p_data[1];
+
+        gf128_mul(x, x, h)
+        
+        /* Increment p_data by 0x10 bytes. */
+        p_data += 2;
+        data_size -= 0x10;
+    }
+    
+    /* Nintendo's code *discards all data in the last block* if unaligned. */
+    /* And treats that block as though it were all-zero. */
+    /* This is a bug, they just forget to XOR with the copy of the last block they save. */
+    if (data_size & 0xF) {
+        gf128_mul(x, x, h)
+    }
+    
+    /* Due to a Nintendo bug, the wrong QWORD gets XOR'd in the "final output block" case. */
+    if (encrypt) {
+        p_x[1] ^= (uint64_t)(total_size << 3);
+    } else {
+        p_x[0] ^= (uint64_t)(total_size << 3);
+    }
+    
+    gf128_mul(x, x, h)
+    
+    /* If final output block, XOR with encrypted J block. */
+    if (encrypt) {
+        se_aes_ecb_encrypt_block(KEYSLOT_SWITCH_TEMPKEY, h, 0x10, j_block, 0x10);
+        for (unsigned int i = 0; i < 0x10; i++) {
+            x[i] ^= h[i];
+        }
+    }
+    
+    /* Copy output. */
+    for (unsigned int i = 0; i < 0x10; i++) {
+        ((uint8_t *)dst)[i] = x[i];
+    }
+    
+}
+
+
+/* This function is a doozy. It decrypts and validates a (non-standard) AES-GCM wrapped keypair. */
+int gcm_decrypt_key(unsigned int keyslot, void *dst, size_t dst_size, const void *src, size_t src_size, const void *sealed_kek, size_t kek_size, const void *wrapped_key, size_t key_size, unsigned int usecase, int is_personalized) {
+    
+    
+    if (is_personalized == 0) {
+        /* Devkit keys use a different keyformat without a MAC/Device ID. */
+        if (src_size <= 0x10 || src_size - 0x10 > dst_size) {
+            panic();
+        }
+    } else {
+        if (src_size <= 0x30 || src_size - 0x20 > dst_size) {
+            panic();
+        }
+    }
+    
+    /* Unwrap the key */
+    unseal_key(KEYSLOT_SWITCH_TEMPKEY, sealed_kek, kek_size, usecase);
+    decrypt_data_into_keyslot(KEYSLOT_SWITCH_TEMPKEY, KEYSLOT_SWITCH_TEMPKEY, wrapped_key, key_size);
+    
+    /* Decrypt the GCM keypair, AES-CTR with CTR = blob[:0x10]. */
+    se_aes_ctr_crypt(KEYSLOT_SWITCH_TEMPKEY, dst, dst_size, src + 0x10, src_size - 0x10, src, 0x10);
+
+    
+    if (is_personalized == 0) {
+        /* Devkit non-personalized keys have no further authentication. */
+        return src_size - 0x10;
+    }
+    
+    /* J = GHASH(CTR); */
+    uint8_t j_block[0x10];
+    ghash(j_block, src, 0x10, NULL, 0);
+    
+    /* MAC = GHASH(CTR) ^ ENCRYPT(J) */
+    uint8_t calc_mac[0x10];
+    ghash(calc_mac, dst, src_size - 0x20, j_block, 1);
+    
+    /* Const-time memcmp. */
+    int different = 0;
+    for (unsigned int i = 0; i < 0x10; i++) {
+        different |= src[src_size - 0x10  + i] ^ calc_mac[i];
+    }
+    if (different) {
+        return 0;
+    }
+    
+    /* TODO: Validate Device ID matches in blob data from fuses. */
+    
+    return src_size - 0x30;
+}

exosphere/gcm.h

@@ -0,0 +1,8 @@
+#ifndef EXOSPHERE_GCM_H
+#define EXOSPHERE_GCM_H
+
+#include <stdint.h>
+
+int gcm_decrypt_key(unsigned int keyslot, void *dst, size_t dst_size, const void *src, size_t src_size, const void *sealed_kek, size_t kek_size, const void *wrapped_key, size_t key_size, unsigned int usecase, int is_personalized);
+
+#endif

exosphere/smc_user.c

@@ -126,11 +126,11 @@ uint32_t user_generate_aes_kek(smc_args_t *args) {
     
     uint64_t is_recovery_boot = configitem_is_recovery_boot();
     
-    /* Mask 2 is only allowed when booted normally. */
+    /* Mask 2 is only allowed when booted from recovery. */
     if (mask_id == 2 && is_recovery_boot == 0) {
         return 2;
     }
-    /* Mask 1 is only allowed when booted from recovery. */
+    /* Mask 1 is only allowed when booted normally. */
     if (mask_id == 1 && is_recovery_boot != 0) {
         return 2;
     }