diff --git a/hardware/Crypto.c b/hardware/Crypto.c
index faaaad2..05b32b6 100644
--- a/hardware/Crypto.c
+++ b/hardware/Crypto.c
@@ -1,29 +1,54 @@
 #include "Crypto.h"
 
-uint8_t active_key[16];
-uint8_t active_iv[16];
+bool encryption_enabled = false;
+uint8_t active_key[CRYPTO_KEY_SIZE];
+uint8_t active_iv[CRYPTO_KEY_SIZE];
 
 aes_128_context_t context;
-uint8_t current_vector[16];
+uint8_t current_vector[CRYPTO_KEY_SIZE];
+uint32_t entropy;
+uint32_t entropy_index = 0;
+bool entropy_loaded = false;
+uint8_t ivs_generated = 0;
+
+FIL crypto_fp;						// File buffer
+char crypto_fb[CRYPTO_KEY_SIZE];	// File read buffer
+FRESULT crypto_fr;					// Result codes
 
 void crypto_init(void) {
-	crypto_test();
-	return;
+	encryption_enabled = false;
+
+	if (load_key()) {
+		if (load_entropy_index() && load_entropy()) {
+			encryption_enabled = true;
+		}
+	}
+
+	if (encryption_enabled) {
+		// TODO: Set flags for crypto enabled
+
+		// TODO: Remove
+		// for (uint8_t i = 0; i < 130; i++) {
+		// 	crypto_test();
+		// }
+	} else {
+		LED_indicate_error_crypto();
+	}
 }
 
-void crypto_prepare(uint8_t key[16], uint8_t initialization_vector[16]) {
+void crypto_prepare(uint8_t key[CRYPTO_KEY_SIZE], uint8_t initialization_vector[CRYPTO_KEY_SIZE]) {
   // Initialise the context with the key
   aes_128_init(&context, key);
 
   // Copy the IV into the current vector array
-  memcpy(current_vector, initialization_vector, 16);
+  memcpy(current_vector, initialization_vector, CRYPTO_KEY_SIZE);
 }
 
-void crypto_encrypt_block(uint8_t block[16]) {
+void crypto_encrypt_block(uint8_t block[CRYPTO_KEY_SIZE]) {
   int i;
 
   // XOR the current vector with the block before encrypting
-  for (i = 0; i < 16; i++) {
+  for (i = 0; i < CRYPTO_KEY_SIZE; i++) {
     block[i] ^= current_vector[i];
   }
 
@@ -31,36 +56,208 @@ void crypto_encrypt_block(uint8_t block[16]) {
   aes_128_encrypt(&context, block);
 
   // Copy the cipher output to the current vector
-  memcpy(current_vector, block, 16);
+  memcpy(current_vector, block, CRYPTO_KEY_SIZE);
 }
 
-void crypto_decrypt_block(uint8_t block[16]) {
-  uint8_t temp_vector[16];
+void crypto_decrypt_block(uint8_t block[CRYPTO_KEY_SIZE]) {
+  uint8_t temp_vector[CRYPTO_KEY_SIZE];
   int i;
 
   // Copy the cipher output to the temporary vector
-  memcpy(temp_vector, block, 16);
+  memcpy(temp_vector, block, CRYPTO_KEY_SIZE);
 
   // Decrypt the block
   aes_128_decrypt(&context, block);
 
   // XOR the output with the current vector to fully decrypt
-  for (i = 0; i < 16; i++) {
+  for (i = 0; i < CRYPTO_KEY_SIZE; i++) {
     block[i] ^= current_vector[i];
   }
 
   // Copy the temporary vector to the current vector
-  memcpy(current_vector, temp_vector, 16);
+  memcpy(current_vector, temp_vector, CRYPTO_KEY_SIZE);
 }
 
-void load_key(void) {
-	// TODO: implement
+bool load_entropy_index(void) {
+	if (sd_mounted()) {
+		crypto_fr = f_open(&crypto_fp, PATH_ENTROPY_INDEX, FA_READ);
+		if (crypto_fr == FR_NO_FILE) {
+			//printf("Entropy index file does not exist\r\n");
+			f_close(&crypto_fp);
+			crypto_fr = f_open(&crypto_fp, PATH_ENTROPY_INDEX, FA_CREATE_NEW | FA_WRITE);
+
+			if (crypto_fr == FR_OK) {
+				entropy_index = 0x00000000;
+				memcpy(crypto_fb, &entropy_index, sizeof(entropy_index));
+				
+				UINT written = 0;
+				crypto_fr = f_write(&crypto_fp, crypto_fb, sizeof(entropy_index), &written);
+				f_close(&crypto_fp);
+				
+				if (crypto_fr == FR_OK && written == sizeof(entropy_index)) {
+					//printf("Wrote new index to index file\r\n");
+				} else {
+					//printf("Could not write index to index file\r\n");
+				}
+			} else {
+				//printf("Could not create index file\r\n");
+			}
+
+			crypto_fr = f_open(&crypto_fp, PATH_ENTROPY_INDEX, FA_READ);
+		}
+
+		if (crypto_fr == FR_OK) {
+			//printf("Opened entropy index file\r\n");
+			UINT read = 0;
+			crypto_fr = f_read(&crypto_fp, crypto_fb, sizeof(entropy_index), &read);
+			f_close(&crypto_fp);
+			if (crypto_fr == FR_OK && read == sizeof(entropy_index)) {
+				memcpy(&entropy_index, crypto_fb, sizeof(entropy_index));
+				//printf("Entropy index is now: %lX\r\n", entropy_index);
+				return true;
+			}
+		} else {
+			//printf("Error opening entropy index file\r\n");
+		}
+
+	}
+
+	f_close(&crypto_fp);
+	return false;
 }
 
-void generate_iv(void) {
-	// TODO: implement
+bool update_entropy_index(void) {
+	crypto_fr = f_open(&crypto_fp, PATH_ENTROPY_INDEX, FA_WRITE);
+	if (crypto_fr == FR_OK) {
+		entropy_index += sizeof(entropy);
+		memcpy(crypto_fb, &entropy_index, sizeof(entropy_index));
+
+		UINT written = 0;
+		crypto_fr = f_write(&crypto_fp, crypto_fb, sizeof(entropy_index), &written);
+
+		if (crypto_fr == FR_OK && written == sizeof(entropy_index)) {
+			return true;
+		}
+	}
+	return false;
 }
 
+bool load_entropy(void) {
+	if (sd_mounted()) {
+		if (update_entropy_index()) {
+			crypto_fr = f_open(&crypto_fp, PATH_ENTROPY_SOURCE, FA_READ);
+			if (crypto_fr == FR_OK) {
+				uint32_t fsize = f_size(&crypto_fp);
+				//uint32_t fpoint = crypto_fp.fptr;
+
+				//printf("Opened entropy file\r\n\tSize is %lu\r\n\tPointer is at %lX \r\n\tSeeking to index: %lX\r\n", fsize, fpoint, entropy_index);
+
+				crypto_fr = f_lseek(&crypto_fp, entropy_index);
+
+				//fpoint = crypto_fp.fptr;
+				//printf("After seek, pointer is now at %lX\r\n", fpoint);
+
+				if (crypto_fr == FR_OK && crypto_fp.fptr < fsize-sizeof(entropy)) {
+					UINT read = 0;
+					crypto_fr = f_read(&crypto_fp, crypto_fb, sizeof(entropy), &read);
+					f_close(&crypto_fp);
+
+					if (crypto_fr == FR_OK) {
+						memcpy(&entropy, crypto_fb, sizeof(entropy));
+						//printf("Read entropy from SD: %lX\r\n", entropy);
+						srandom(entropy);
+						entropy_loaded = true;
+						ivs_generated = 0;
+						return true;
+					} else {
+						//printf("Could not read entropy data from SD\r\n");
+					}
+
+				} else {
+					f_close(&crypto_fp);
+					//printf("Could not seek in index file, entropy exhausted\r\n");
+					LED_indicate_error_crypto();
+				}
+			}
+		}
+	}
+
+	f_close(&crypto_fp);
+	return false;
+}
+
+bool load_key(void) {
+	if (sd_mounted()) {
+		crypto_fr = f_open(&crypto_fp, PATH_AES_128_KEY, FA_READ);
+		if (crypto_fr == FR_OK) {
+			//printf("File open\r\n");
+			UINT read = 0;
+			crypto_fr = f_read(&crypto_fp, crypto_fb, CRYPTO_KEY_SIZE, &read);
+			f_close(&crypto_fp);
+
+			if (crypto_fr == FR_OK && read == CRYPTO_KEY_SIZE) {
+				//printf("Loaded AES-128 Key: ");
+				for (uint8_t i = 0; i < 16; i++) {
+					active_key[i] = crypto_fb[i];
+					//printf("%X ", crypto_fb[i]);
+				}
+				//printf("\r\n");	
+				return true;
+			} else {
+				//printf("Error %d reading file, read %d bytes.\r\n", crypto_fr, read);
+			}
+		} else {
+			//printf("Could not open file\r\n");
+		}
+	} else {
+		//printf("SD not mounted\r\n");
+	}
+
+	return false;
+}
+
+bool generate_iv(void) {
+	if (entropy_loaded) {
+		for (uint8_t i = 0; i < 16; i++) {
+			active_iv[i] = (uint8_t)random();
+		}
+		ivs_generated++;
+
+		// TODO: remove
+		/*printf("Generated IV: ");
+		for (uint8_t i = 0; i < 16; i++) {
+			printf("%X ", active_iv[i]);
+		}
+		printf("\r\n");*/
+
+		if (ivs_generated >= MAX_IVS_PER_ENTROPY_BLOCK) {
+			load_entropy();
+		}
+
+		return true;
+	} else {
+		return false;
+	}
+}
+
+// TODO: Remove this
 void crypto_test(void) {
+	generate_iv();
+
+	uint8_t work_block[16];
+	memset(work_block, 0x70, 16);
+	work_block[15] = 0x00;
+
+	//printf("Work block plaintext:  ===%s===\r\n", work_block);
 	
-}
\ No newline at end of file
+	crypto_prepare(active_key, active_iv);
+	crypto_encrypt_block(work_block);
+	//printf("Work block ciphertext: ===%s===\r\n", work_block);
+
+	crypto_prepare(active_key, active_iv);
+	crypto_decrypt_block(work_block);
+	printf("Work block plaintext:  ===%s===\r\n", work_block);
+
+}
+
+// TODO: test entropy exhaustion
\ No newline at end of file
diff --git a/hardware/Crypto.h b/hardware/Crypto.h
index afdc4bb..703a03a 100644
--- a/hardware/Crypto.h
+++ b/hardware/Crypto.h
@@ -5,10 +5,24 @@
 #include <stdlib.h>
 #include <stdbool.h>
 #include <stdio.h>
-#include "crypto/aes.h"
+#include "hardware/crypto/aes.h"
+#include "hardware/LED.h"
+#include "hardware/SD.h"
+
+#define PATH_ENTROPY_INDEX "OpenModem/entropy.index"
+#define PATH_ENTROPY_SOURCE "OpenModem/entropy.source"
+#define PATH_AES_128_KEY "OpenModem/aes128.key"
+
+#define CRYPTO_KEY_SIZE_BITS 128
+#define CRYPTO_KEY_SIZE (CRYPTO_KEY_SIZE_BITS/8)
+#define MAX_IVS_PER_ENTROPY_BLOCK 128
 
 void crypto_init(void);
 void crypto_test(void);
 
+bool load_key(void);
+bool load_entropy(void);
+bool load_entropy_index(void);
+
 #endif
 
diff --git a/hardware/LED.c b/hardware/LED.c
index d6790ca..f573a5a 100644
--- a/hardware/LED.c
+++ b/hardware/LED.c
@@ -52,4 +52,15 @@ void update_led_status(void) {
     } else {
         led_status_ticks++;
     }
+}
+
+void LED_indicate_error_crypto(void) {
+    while (true) {
+        LED_COM_ON();
+        LED_STATUS_OFF();
+        delay_ms(500);
+        LED_COM_OFF();
+        LED_STATUS_ON();
+        delay_ms(500);
+    }
 }
\ No newline at end of file
diff --git a/hardware/LED.h b/hardware/LED.h
index 341626b..3b5d7b6 100644
--- a/hardware/LED.h
+++ b/hardware/LED.h
@@ -19,4 +19,6 @@ void LED_COM_ON(void);
 void LED_COM_OFF(void);
 void update_led_status(void);
 
+void LED_indicate_error_crypto(void);
+
 #endif
\ No newline at end of file
diff --git a/hardware/SD.c b/hardware/SD.c
index 64becaf..ae53222 100644
--- a/hardware/SD.c
+++ b/hardware/SD.c
@@ -1,4 +1,5 @@
 #include "SD.h"
+#include "hardware/Crypto.h"
 
 FATFS sdfs;
 
@@ -24,6 +25,7 @@ void sd_init(void) {
 
 void sd_automounted_hook(void) {
     sd_statuschange_indication(1);
+    crypto_init();
 }
 
 void sd_autounmounted_hook(void) {
diff --git a/hardware/SD.h b/hardware/SD.h
index f56c80c..a2ef809 100644
--- a/hardware/SD.h
+++ b/hardware/SD.h
@@ -23,4 +23,6 @@ void sd_automount(void);
 void sd_autounmount(void);
 void sd_statuschange_indication(uint8_t pattern);
 
+bool sd_mounted(void);
+
 #endif
\ No newline at end of file
diff --git a/main.c b/main.c
index a92adc6..8b27440 100755
--- a/main.c
+++ b/main.c
@@ -70,7 +70,6 @@ void init(void) {
     ax25_init(&AX25, &modem, &modem.fd, ax25_callback);
     kiss_init(&AX25, &modem, &serial);
     sd_init();
-    crypto_init();
     bluetooth_init();
     gps_init(&serial);
     usrio_init();