diff --git a/bitchat/Nostr/XChaCha20Poly1305Compat.swift b/bitchat/Nostr/XChaCha20Poly1305Compat.swift
index 44f1ca97..13794508 100644
--- a/bitchat/Nostr/XChaCha20Poly1305Compat.swift
+++ b/bitchat/Nostr/XChaCha20Poly1305Compat.swift
@@ -5,16 +5,27 @@ import CryptoKit
 /// Implements HChaCha20 to derive a subkey and reduces the 24-byte nonce to a 12-byte nonce
 /// as per XChaCha20 construction.
 enum XChaCha20Poly1305Compat {
+
+    /// Errors that can occur during XChaCha20-Poly1305 operations
+    enum Error: Swift.Error {
+        case invalidKeyLength(expected: Int, got: Int)
+        case invalidNonceLength(expected: Int, got: Int)
+    }
+
     struct SealBox {
         let ciphertext: Data
         let tag: Data
     }
 
     static func seal(plaintext: Data, key: Data, nonce24: Data, aad: Data? = nil) throws -> SealBox {
-        precondition(key.count == 32, "XChaCha20 key must be 32 bytes")
-        precondition(nonce24.count == 24, "XChaCha20 nonce must be 24 bytes")
+        guard key.count == 32 else {
+            throw Error.invalidKeyLength(expected: 32, got: key.count)
+        }
+        guard nonce24.count == 24 else {
+            throw Error.invalidNonceLength(expected: 24, got: nonce24.count)
+        }
 
-        let subkey = hchacha20(key: key, nonce16: nonce24.prefix(16))
+        let subkey = try hchacha20(key: key, nonce16: Data(nonce24.prefix(16)))
         let nonce12 = derive12ByteNonce(from24: nonce24)
         let chachaKey = SymmetricKey(data: subkey)
         let nonce = try ChaChaPoly.Nonce(data: nonce12)
@@ -23,10 +34,14 @@ enum XChaCha20Poly1305Compat {
     }
 
     static func open(ciphertext: Data, tag: Data, key: Data, nonce24: Data, aad: Data? = nil) throws -> Data {
-        precondition(key.count == 32, "XChaCha20 key must be 32 bytes")
-        precondition(nonce24.count == 24, "XChaCha20 nonce must be 24 bytes")
+        guard key.count == 32 else {
+            throw Error.invalidKeyLength(expected: 32, got: key.count)
+        }
+        guard nonce24.count == 24 else {
+            throw Error.invalidNonceLength(expected: 24, got: nonce24.count)
+        }
 
-        let subkey = hchacha20(key: key, nonce16: nonce24.prefix(16))
+        let subkey = try hchacha20(key: key, nonce16: Data(nonce24.prefix(16)))
         let nonce12 = derive12ByteNonce(from24: nonce24)
         let chachaKey = SymmetricKey(data: subkey)
         let box = try ChaChaPoly.SealedBox(nonce: ChaChaPoly.Nonce(data: nonce12), ciphertext: ciphertext, tag: tag)
@@ -43,10 +58,14 @@ enum XChaCha20Poly1305Compat {
         return out
     }
 
-    private static func hchacha20(key: Data, nonce16: Data) -> Data {
+    private static func hchacha20(key: Data, nonce16: Data) throws -> Data {
         // HChaCha20 based on the original ChaCha20 core with a 16-byte nonce.
-        precondition(key.count == 32)
-        precondition(nonce16.count == 16)
+        guard key.count == 32 else {
+            throw Error.invalidKeyLength(expected: 32, got: key.count)
+        }
+        guard nonce16.count == 16 else {
+            throw Error.invalidNonceLength(expected: 16, got: nonce16.count)
+        }
 
         // Constants "expand 32-byte k"
         var state: [UInt32] = [
diff --git a/bitchatTests/XChaCha20Poly1305CompatTests.swift b/bitchatTests/XChaCha20Poly1305CompatTests.swift
new file mode 100644
index 00000000..9b607a9b
--- /dev/null
+++ b/bitchatTests/XChaCha20Poly1305CompatTests.swift
@@ -0,0 +1,222 @@
+//
+// XChaCha20Poly1305CompatTests.swift
+// bitchatTests
+//
+// Tests for XChaCha20-Poly1305 encryption with proper error handling.
+// This is free and unencumbered software released into the public domain.
+//
+
+import Testing
+import struct Foundation.Data
+@testable import bitchat
+
+struct XChaCha20Poly1305CompatTests {
+
+    @Test func sealAndOpenRoundtrip() throws {
+        let plaintext = "Hello, XChaCha20-Poly1305!".data(using: .utf8)!
+        let key = Data(repeating: 0x42, count: 32)
+        let nonce = Data(repeating: 0x24, count: 24)
+
+        let sealed = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: key, nonce24: nonce)
+        let decrypted = try XChaCha20Poly1305Compat.open(
+            ciphertext: sealed.ciphertext,
+            tag: sealed.tag,
+            key: key,
+            nonce24: nonce
+        )
+
+        #expect(decrypted == plaintext)
+    }
+
+    @Test func sealAndOpenWithAAD() throws {
+        let plaintext = "Secret message".data(using: .utf8)!
+        let key = Data(repeating: 0xAB, count: 32)
+        let nonce = Data(repeating: 0xCD, count: 24)
+        let aad = "additional authenticated data".data(using: .utf8)!
+
+        let sealed = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: key, nonce24: nonce, aad: aad)
+        let decrypted = try XChaCha20Poly1305Compat.open(
+            ciphertext: sealed.ciphertext,
+            tag: sealed.tag,
+            key: key,
+            nonce24: nonce,
+            aad: aad
+        )
+
+        #expect(decrypted == plaintext)
+    }
+
+    @Test func sealProducesDifferentCiphertextWithDifferentNonces() throws {
+        let plaintext = "Same plaintext".data(using: .utf8)!
+        let key = Data(repeating: 0x42, count: 32)
+        let nonce1 = Data(repeating: 0x01, count: 24)
+        let nonce2 = Data(repeating: 0x02, count: 24)
+
+        let sealed1 = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: key, nonce24: nonce1)
+        let sealed2 = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: key, nonce24: nonce2)
+
+        #expect(sealed1.ciphertext != sealed2.ciphertext)
+    }
+
+    @Test func sealThrowsOnShortKey() {
+        let plaintext = "Test".data(using: .utf8)!
+        let shortKey = Data(repeating: 0x42, count: 16)
+        let nonce = Data(repeating: 0x24, count: 24)
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: shortKey, nonce24: nonce)
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+
+    @Test func sealThrowsOnLongKey() {
+        let plaintext = "Test".data(using: .utf8)!
+        let longKey = Data(repeating: 0x42, count: 64)
+        let nonce = Data(repeating: 0x24, count: 24)
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: longKey, nonce24: nonce)
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+
+    @Test func sealThrowsOnEmptyKey() {
+        let plaintext = "Test".data(using: .utf8)!
+        let emptyKey = Data()
+        let nonce = Data(repeating: 0x24, count: 24)
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: emptyKey, nonce24: nonce)
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+
+    @Test func openThrowsOnInvalidKeyLength() {
+        let ciphertext = Data(repeating: 0x00, count: 16)
+        let tag = Data(repeating: 0x00, count: 16)
+        let shortKey = Data(repeating: 0x42, count: 31)
+        let nonce = Data(repeating: 0x24, count: 24)
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.open(ciphertext: ciphertext, tag: tag, key: shortKey, nonce24: nonce)
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+
+    @Test func sealThrowsOnShortNonce() {
+        let plaintext = "Test".data(using: .utf8)!
+        let key = Data(repeating: 0x42, count: 32)
+        let shortNonce = Data(repeating: 0x24, count: 12)
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: key, nonce24: shortNonce)
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+
+    @Test func sealThrowsOnLongNonce() {
+        let plaintext = "Test".data(using: .utf8)!
+        let key = Data(repeating: 0x42, count: 32)
+        let longNonce = Data(repeating: 0x24, count: 32)
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: key, nonce24: longNonce)
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+
+    @Test func sealThrowsOnEmptyNonce() {
+        let plaintext = "Test".data(using: .utf8)!
+        let key = Data(repeating: 0x42, count: 32)
+        let emptyNonce = Data()
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: key, nonce24: emptyNonce)
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+
+    @Test func openThrowsOnInvalidNonceLength() {
+        let ciphertext = Data(repeating: 0x00, count: 16)
+        let tag = Data(repeating: 0x00, count: 16)
+        let key = Data(repeating: 0x42, count: 32)
+        let shortNonce = Data(repeating: 0x24, count: 23)
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.open(ciphertext: ciphertext, tag: tag, key: key, nonce24: shortNonce)
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+
+    @Test func openFailsWithWrongKey() throws {
+        let plaintext = "Secret".data(using: .utf8)!
+        let correctKey = Data(repeating: 0x42, count: 32)
+        let wrongKey = Data(repeating: 0x43, count: 32)
+        let nonce = Data(repeating: 0x24, count: 24)
+
+        let sealed = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: correctKey, nonce24: nonce)
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.open(
+                ciphertext: sealed.ciphertext,
+                tag: sealed.tag,
+                key: wrongKey,
+                nonce24: nonce
+            )
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+
+    @Test func openFailsWithTamperedCiphertext() throws {
+        let plaintext = "Secret".data(using: .utf8)!
+        let key = Data(repeating: 0x42, count: 32)
+        let nonce = Data(repeating: 0x24, count: 24)
+
+        let sealed = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: key, nonce24: nonce)
+
+        // Create tampered ciphertext by changing first byte
+        var tamperedBytes = [UInt8](sealed.ciphertext)
+        tamperedBytes[0] = tamperedBytes[0] ^ 0xFF
+        let tampered = Data(tamperedBytes)
+
+        var didThrow = false
+        do {
+            _ = try XChaCha20Poly1305Compat.open(
+                ciphertext: tampered,
+                tag: sealed.tag,
+                key: key,
+                nonce24: nonce
+            )
+        } catch {
+            didThrow = true
+        }
+        #expect(didThrow)
+    }
+}