diff --git a/src/main/java/com/southernstorm/noise/protocol/AESGCMFallbackCipherState.java b/src/main/java/com/southernstorm/noise/protocol/AESGCMFallbackCipherState.java
index 7cd2b74..f627be3 100644
--- a/src/main/java/com/southernstorm/noise/protocol/AESGCMFallbackCipherState.java
+++ b/src/main/java/com/southernstorm/noise/protocol/AESGCMFallbackCipherState.java
@@ -185,10 +185,11 @@ class AESGCMFallbackCipherState implements CipherState {
 			byte[] ciphertext, int ciphertextOffset, int length)
 			throws ShortBufferException {
 		int space;
-		if (ciphertextOffset > ciphertext.length)
-			space = 0;
-		else
-			space = ciphertext.length - ciphertextOffset;
+		if (ciphertextOffset < 0 || ciphertextOffset > ciphertext.length)
+			throw new IllegalArgumentException();
+		if (length < 0 || plaintextOffset < 0 || plaintextOffset > plaintext.length)
+			throw new IllegalArgumentException();
+		space = ciphertext.length - ciphertextOffset;
 		if (!haskey) {
 			// The key is not set yet - return the plaintext as-is.
 			if (length > space)
@@ -214,16 +215,15 @@ class AESGCMFallbackCipherState implements CipherState {
 			int ciphertextOffset, byte[] plaintext, int plaintextOffset,
 			int length) throws ShortBufferException, BadPaddingException {
 		int space;
-		if (ciphertextOffset > ciphertext.length)
-			space = 0;
+		if (ciphertextOffset < 0 || ciphertextOffset > ciphertext.length)
+			throw new IllegalArgumentException();
 		else
 			space = ciphertext.length - ciphertextOffset;
 		if (length > space)
 			throw new ShortBufferException();
-		if (plaintextOffset > plaintext.length)
-			space = 0;
-		else
-			space = plaintext.length - plaintextOffset;
+		if (length < 0 || plaintextOffset < 0 || plaintextOffset > plaintext.length)
+			throw new IllegalArgumentException();
+		space = plaintext.length - plaintextOffset;
 		if (!haskey) {
 			// The key is not set yet - return the ciphertext as-is.
 			if (length > space)
diff --git a/src/main/java/com/southernstorm/noise/protocol/AESGCMOnCtrCipherState.java b/src/main/java/com/southernstorm/noise/protocol/AESGCMOnCtrCipherState.java
index deada67..df40945 100644
--- a/src/main/java/com/southernstorm/noise/protocol/AESGCMOnCtrCipherState.java
+++ b/src/main/java/com/southernstorm/noise/protocol/AESGCMOnCtrCipherState.java
@@ -218,10 +218,11 @@ class AESGCMOnCtrCipherState implements CipherState {
 			byte[] ciphertext, int ciphertextOffset, int length)
 			throws ShortBufferException {
 		int space;
-		if (ciphertextOffset > ciphertext.length)
-			space = 0;
-		else
-			space = ciphertext.length - ciphertextOffset;
+		if (ciphertextOffset < 0 || ciphertextOffset > ciphertext.length)
+			throw new IllegalArgumentException();
+		if (length < 0 || plaintextOffset < 0 || plaintextOffset > plaintext.length)
+			throw new IllegalArgumentException();
+		space = ciphertext.length - ciphertextOffset;
 		if (keySpec == null) {
 			// The key is not set yet - return the plaintext as-is.
 			if (length > space)
@@ -262,16 +263,15 @@ class AESGCMOnCtrCipherState implements CipherState {
 			int ciphertextOffset, byte[] plaintext, int plaintextOffset,
 			int length) throws ShortBufferException, BadPaddingException {
 		int space;
-		if (ciphertextOffset > ciphertext.length)
-			space = 0;
+		if (ciphertextOffset < 0 || ciphertextOffset > ciphertext.length)
+			throw new IllegalArgumentException();
 		else
 			space = ciphertext.length - ciphertextOffset;
 		if (length > space)
 			throw new ShortBufferException();
-		if (plaintextOffset > plaintext.length)
-			space = 0;
-		else
-			space = plaintext.length - plaintextOffset;
+		if (length < 0 || plaintextOffset < 0 || plaintextOffset > plaintext.length)
+			throw new IllegalArgumentException();
+		space = plaintext.length - plaintextOffset;
 		if (keySpec == null) {
 			// The key is not set yet - return the ciphertext as-is.
 			if (length > space)
diff --git a/src/main/java/com/southernstorm/noise/protocol/ChaChaPolyCipherState.java b/src/main/java/com/southernstorm/noise/protocol/ChaChaPolyCipherState.java
index 25b1a4c..40ce2bc 100644
--- a/src/main/java/com/southernstorm/noise/protocol/ChaChaPolyCipherState.java
+++ b/src/main/java/com/southernstorm/noise/protocol/ChaChaPolyCipherState.java
@@ -214,10 +214,11 @@ class ChaChaPolyCipherState implements CipherState {
 	public int encryptWithAd(byte[] ad, byte[] plaintext, int plaintextOffset,
 			byte[] ciphertext, int ciphertextOffset, int length) throws ShortBufferException {
 		int space;
-		if (ciphertextOffset > ciphertext.length)
-			space = 0;
-		else
-			space = ciphertext.length - ciphertextOffset;
+		if (ciphertextOffset < 0 || ciphertextOffset > ciphertext.length)
+			throw new IllegalArgumentException();
+		if (length < 0 || plaintextOffset < 0 || plaintextOffset > plaintext.length)
+			throw new IllegalArgumentException();
+		space = ciphertext.length - ciphertextOffset;
 		if (!haskey) {
 			// The key is not set yet - return the plaintext as-is.
 			if (length > space)
@@ -241,16 +242,15 @@ class ChaChaPolyCipherState implements CipherState {
 			int ciphertextOffset, byte[] plaintext, int plaintextOffset,
 			int length) throws ShortBufferException, BadPaddingException {
 		int space;
-		if (ciphertextOffset > ciphertext.length)
-			space = 0;
+		if (ciphertextOffset < 0 || ciphertextOffset > ciphertext.length)
+			throw new IllegalArgumentException();
 		else
 			space = ciphertext.length - ciphertextOffset;
 		if (length > space)
 			throw new ShortBufferException();
-		if (plaintextOffset > plaintext.length)
-			space = 0;
-		else
-			space = plaintext.length - plaintextOffset;
+		if (length < 0 || plaintextOffset < 0 || plaintextOffset > plaintext.length)
+			throw new IllegalArgumentException();
+		space = plaintext.length - plaintextOffset;
 		if (!haskey) {
 			// The key is not set yet - return the ciphertext as-is.
 			if (length > space)
diff --git a/src/main/java/com/southernstorm/noise/protocol/CipherState.java b/src/main/java/com/southernstorm/noise/protocol/CipherState.java
index 3168139..74f808b 100644
--- a/src/main/java/com/southernstorm/noise/protocol/CipherState.java
+++ b/src/main/java/com/southernstorm/noise/protocol/CipherState.java
@@ -100,6 +100,8 @@ public interface CipherState extends Destroyable {
 	 * 
 	 * @throws IllegalStateException The nonce has wrapped around.
 	 * 
+	 * @throws IllegalArgumentException One of the parameters is out of range.
+	 *
 	 * The plaintext and ciphertext buffers can be the same for in-place
 	 * encryption.  In that case, plaintextOffset must be identical to
 	 * ciphertextOffset.
@@ -130,6 +132,8 @@ public interface CipherState extends Destroyable {
 	 * 
 	 * @throws IllegalStateException The nonce has wrapped around.
 	 * 
+	 * @throws IllegalArgumentException One of the parameters is out of range.
+	 *
 	 * The plaintext and ciphertext buffers can be the same for in-place
 	 * decryption.  In that case, ciphertextOffset must be identical to
 	 * plaintextOffset.