diff --git a/src/models/backup.model.ts b/src/models/backup.model.ts
index 5050688..27f06b0 100644
--- a/src/models/backup.model.ts
+++ b/src/models/backup.model.ts
@@ -1,7 +1,304 @@
 import { Device, Process, SecretsStore } from "pkg/sdk_client";
 
-export interface BackUp {
-    device: Device,
-    secrets: SecretsStore,
-    processes: Record<string, Process>,
+export interface UserDataBackUp {
+    version: number,
+    exported_at: Date,
+    user_data: {
+        device: Device | string, // string if encrypted
+        secrets: SecretsStore | string, // string if encrypted
+        processes: Record<string, Process> | string, // string if encrypted
+    },
+    metadata: {
+        encrypted: boolean,
+        checksum: string,
+    }
+}
+
+/**
+ * Validates a UserDataBackUp object
+ * @param backup - The backup object to validate
+ * @returns null if valid, error message string if invalid
+ */
+export function isValid(backup: any): string | null {
+    // Check if backup is an object
+    if (!backup || typeof backup !== 'object') {
+        return 'Backup must be a valid object';
+    }
+
+    // Validate version
+    if (typeof backup.version !== 'number') {
+        return 'Version must be a number';
+    }
+    if (backup.version <= 0) {
+        return 'Version must be greater than 0';
+    }
+
+    // Validate exported_at
+    if (!(backup.exported_at instanceof Date)) {
+        return 'exported_at must be a valid Date object';
+    }
+    if (isNaN(backup.exported_at.getTime())) {
+        return 'exported_at must be a valid date';
+    }
+
+    // Validate user_data
+    if (!backup.user_data || typeof backup.user_data !== 'object') {
+        return 'user_data must be a valid object';
+    }
+
+    // Validate metadata
+    if (!backup.metadata || typeof backup.metadata !== 'object') {
+        return 'metadata must be a valid object';
+    }
+
+    if (typeof backup.metadata.encrypted !== 'boolean') {
+        return 'metadata.encrypted must be a boolean';
+    }
+
+    if (typeof backup.metadata.checksum !== 'string') {
+        return 'metadata.checksum must be a string';
+    }
+    if (backup.metadata.checksum.length === 0) {
+        return 'metadata.checksum cannot be empty';
+    }
+
+    // Validate user_data fields based on encryption status
+    const { encrypted } = backup.metadata;
+    const { device, secrets, processes } = backup.user_data;
+
+    // Validate device
+    if (encrypted) {
+        if (typeof device !== 'string') {
+            return 'device must be a string when backup is encrypted';
+        }
+        if (device.length === 0) {
+            return 'device cannot be empty when backup is encrypted';
+        }
+    } else {
+        if (!device || typeof device !== 'object') {
+            return 'device must be a valid object when backup is not encrypted';
+        }
+        // Validate Device structure
+        const deviceError = validateDevice(device);
+        if (deviceError) {
+            return `Invalid device: ${deviceError}`;
+        }
+    }
+
+    // Validate secrets
+    if (encrypted) {
+        if (typeof secrets !== 'string') {
+            return 'secrets must be a string when backup is encrypted';
+        }
+        if (secrets.length === 0) {
+            return 'secrets cannot be empty when backup is encrypted';
+        }
+    } else {
+        if (!secrets || typeof secrets !== 'object') {
+            return 'secrets must be a valid object when backup is not encrypted';
+        }
+        // Validate SecretsStore structure
+        const secretsError = validateSecretsStore(secrets);
+        if (secretsError) {
+            return `Invalid secrets: ${secretsError}`;
+        }
+    }
+
+    // Validate processes
+    if (encrypted) {
+        if (typeof processes !== 'string') {
+            return 'processes must be a string when backup is encrypted';
+        }
+        if (processes.length === 0) {
+            return 'processes cannot be empty when backup is encrypted';
+        }
+    } else {
+        if (!processes || typeof processes !== 'object') {
+            return 'processes must be a valid object when backup is not encrypted';
+        }
+        // Validate processes Record structure
+        const processesError = validateProcessesRecord(processes);
+        if (processesError) {
+            return `Invalid processes: ${processesError}`;
+        }
+    }
+
+    return null; // Valid
+}
+
+/**
+ * Validates a Device object
+ */
+function validateDevice(device: any): string | null {
+    if (!device || typeof device !== 'object') {
+        return 'Device must be a valid object';
+    }
+
+    // Check for required Device properties
+    if (!device.sp_wallet || typeof device.sp_wallet !== 'object') {
+        return 'sp_wallet must be a valid object';
+    }
+
+    // Validate sp_wallet structure (basic validation)
+    if (!device.sp_wallet.sp_address || typeof device.sp_wallet.sp_address !== 'string') {
+        return 'sp_wallet.sp_address must be a non-empty string';
+    }
+
+    // pairing_process_commitment can be null or an object
+    if (device.pairing_process_commitment !== null && 
+        (typeof device.pairing_process_commitment !== 'object' || 
+         typeof device.pairing_process_commitment.txid !== 'string' || 
+         typeof device.pairing_process_commitment.vout !== 'number')) {
+        return 'pairing_process_commitment must be null or a valid OutPoint object with txid (string) and vout (number)';
+    }
+
+    // Validate paired_member
+    if (!device.paired_member || typeof device.paired_member !== 'object') {
+        return 'paired_member must be a valid object';
+    }
+
+    if (!Array.isArray(device.paired_member.sp_addresses)) {
+        return 'paired_member.sp_addresses must be an array';
+    }
+    
+    if (!device.paired_member.sp_addresses.every((addr: any) => typeof addr === 'string')) {
+        return 'All sp_addresses must be strings';
+    }
+
+    return null; // Valid
+}
+
+/**
+ * Validates a SecretsStore object
+ */
+function validateSecretsStore(secrets: any): string | null {
+    if (!secrets || typeof secrets !== 'object') {
+        return 'Secrets must be a valid object';
+    }
+
+    // Validate shared_secrets
+    if (!secrets.shared_secrets || typeof secrets.shared_secrets !== 'object') {
+        return 'shared_secrets must be a valid object';
+    }
+
+    // Validate unconfirmed_secrets
+    if (!Array.isArray(secrets.unconfirmed_secrets)) {
+        return 'unconfirmed_secrets must be an array';
+    }
+
+    // Basic validation of shared_secrets entries
+    for (const [key, value] of Object.entries(secrets.shared_secrets)) {
+        if (typeof key !== 'string') {
+            return 'All shared_secrets keys must be strings';
+        }
+        if (typeof value !== 'string') {
+            return 'All shared_secrets values must be strings';
+        }
+    }
+
+    // Basic validation of unconfirmed_secrets entries
+    for (const secret of secrets.unconfirmed_secrets) {
+        if (typeof secret !== 'string') {
+            return 'All unconfirmed_secrets must be strings';
+        }
+    }
+
+    return null; // Valid
+}
+
+/**
+ * Validates a Record<string, Process> object
+ */
+function validateProcessesRecord(processes: any): string | null {
+    if (!processes || typeof processes !== 'object') {
+        return 'Processes must be a valid object';
+    }
+
+    for (const [key, process] of Object.entries(processes)) {
+        if (typeof key !== 'string') {
+            return 'All process keys must be strings';
+        }
+        const processError = validateProcess(process);
+        if (processError) {
+            return `Invalid process '${key}': ${processError}`;
+        }
+    }
+
+    return null; // Valid
+}
+
+/**
+ * Validates a Process object
+ */
+function validateProcess(process: any): string | null {
+    if (!process || typeof process !== 'object') {
+        return 'Process must be a valid object';
+    }
+
+    if (!Array.isArray(process.states)) {
+        return 'Process states must be an array';
+    }
+
+    // Validate each state in the process
+    for (let i = 0; i < process.states.length; i++) {
+        const stateError = validateProcessState(process.states[i]);
+        if (stateError) {
+            return `Invalid state at index ${i}: ${stateError}`;
+        }
+    }
+
+    return null; // Valid
+}
+
+/**
+ * Validates a ProcessState object
+ */
+function validateProcessState(state: any): string | null {
+    if (!state || typeof state !== 'object') {
+        return 'Process state must be a valid object';
+    }
+
+    // Validate commited_in (OutPoint)
+    if (!state.commited_in || typeof state.commited_in !== 'object') {
+        return 'commited_in must be a valid object';
+    }
+
+    if (typeof state.commited_in.txid !== 'string') {
+        return 'commited_in.txid must be a string';
+    }
+    if (typeof state.commited_in.vout !== 'number') {
+        return 'commited_in.vout must be a number';
+    }
+
+    // Validate pcd_commitment
+    if (!state.pcd_commitment || typeof state.pcd_commitment !== 'object') {
+        return 'pcd_commitment must be a valid object';
+    }
+
+    // Validate state_id
+    if (typeof state.state_id !== 'string') {
+        return 'state_id must be a string';
+    }
+
+    // Validate keys
+    if (!state.keys || typeof state.keys !== 'object') {
+        return 'keys must be a valid object';
+    }
+
+    // Validate validation_tokens
+    if (!Array.isArray(state.validation_tokens)) {
+        return 'validation_tokens must be an array';
+    }
+
+    // Validate public_data
+    if (!state.public_data || typeof state.public_data !== 'object') {
+        return 'public_data must be a valid object';
+    }
+
+    // Validate roles
+    if (!state.roles || typeof state.roles !== 'object') {
+        return 'roles must be a valid object';
+    }
+
+    return null; // Valid
 }