diff --git a/core/crypto/_chacha20/chacha20.odin b/core/crypto/_chacha20/chacha20.odin
index 7d94d8a95..40ca9fb25 100644
--- a/core/crypto/_chacha20/chacha20.odin
+++ b/core/crypto/_chacha20/chacha20.odin
@@ -1,5 +1,6 @@
 package _chacha20
 
+import "base:intrinsics"
 import "core:crypto"
 import "core:encoding/endian"
 import "core:math/bits"
@@ -108,11 +109,16 @@ check_counter_limit :: proc(ctx: ^Context, nr_blocks: int) {
 
 	ctr_ok: bool
 	if ctx._is_ietf_flavor {
-		ctr_ok = u64(ctx._s[12]) + u64(nr_blocks) <= MAX_CTR_IETF
+		if intrinsics.unlikely(ctx._s[12] == MAX_CTR_IETF && nr_blocks > 1) {
+			// Allow the final block.
+			ctr_ok = false
+		} else {
+			ctr_ok = u64(ctx._s[12]) + u64(nr_blocks) <= MAX_CTR_IETF
+		}
 	} else {
 		ctr := (u64(ctx._s[13]) << 32) | u64(ctx._s[12])
-		_, carry := bits.add_u64(ctr, u64(nr_blocks), 0)
-		ctr_ok = carry == 0
+		new_ctr, carry := bits.add_u64(ctr, u64(nr_blocks), 0)
+		ctr_ok = carry == 0 || new_ctr != 0 // Allow the final block.
 	}
 
 	ensure(ctr_ok, "crypto/chacha20: maximum (X)ChaCha20 keystream per IV reached")
diff --git a/core/crypto/kmac/kmac.odin b/core/crypto/kmac/kmac.odin
index f0c27739a..f09176edc 100644
--- a/core/crypto/kmac/kmac.odin
+++ b/core/crypto/kmac/kmac.odin
@@ -35,6 +35,10 @@ sum :: proc(sec_strength: int, dst, msg, key, domain_sep: []byte) {
 // strength, key and domain separator over msg and return true if and only if (⟺) the
 // tag is valid.
 verify :: proc(sec_strength: int, tag, msg, key, domain_sep: []byte, allocator := context.temp_allocator) -> bool {
+	if len(tag) < MIN_TAG_SIZE {
+		return false
+	}
+
 	derived_tag := make([]byte, len(tag), allocator)
 	defer(delete(derived_tag))
 
diff --git a/core/crypto/mlkem/api.odin b/core/crypto/mlkem/api.odin
index 3e3956ba8..6cbbd3249 100644
--- a/core/crypto/mlkem/api.odin
+++ b/core/crypto/mlkem/api.odin
@@ -269,7 +269,7 @@ params :: proc(k: ^$T) -> Parameters where (T == Encapsulation_Key || T == Decap
 @(require_results)
 key_size :: proc(k: ^$T) -> int where (T == Encapsulation_Key || T == Decapsulation_Key) {
 	when T == Encapsulation_Key {
-		return ENCAPSULATION_KEY_SIZES[k.pke_ek.k]
+		return ENCAPSULATION_KEY_SIZES[params(k)]
 	} else {
 		return DECAPSULATION_KEY_SEED_SIZE
 	}
diff --git a/core/crypto/noise/protocol.odin b/core/crypto/noise/protocol.odin
index 7327e638b..4bbe858da 100644
--- a/core/crypto/noise/protocol.odin
+++ b/core/crypto/noise/protocol.odin
@@ -217,7 +217,7 @@ cipherstate_encrypt_with_ad :: proc(self: ^Cipher_State, ad, plaintext, dst: []b
 		}
 		_encrypt(&self.ctx, self.n, ad, plaintext, dst)
 		self.n += 1
-		if self.n == 0 {
+		if self.n == max(u64) {
 			self.n_exhausted = true
 		}
 	} else {
@@ -249,7 +249,7 @@ cipherstate_decrypt_with_ad :: proc(self: ^Cipher_State, ad, ciphertext, dst: []
 			return nil, status
 		}
 		self.n += 1
-		if self.n == 0 {
+		if self.n == max(u64) {
 			self.n_exhausted = true
 		}
 	} else {
diff --git a/core/crypto/pbkdf2/pbkdf2.odin b/core/crypto/pbkdf2/pbkdf2.odin
index c27ec4aa2..ef7fda0d5 100644
--- a/core/crypto/pbkdf2/pbkdf2.odin
+++ b/core/crypto/pbkdf2/pbkdf2.odin
@@ -19,6 +19,8 @@ derive :: proc(
 	iterations: u32,
 	dst: []byte,
 ) {
+	ensure(iterations > 0, "crypto/pbkdf2: non-zero iterations required")
+	
 	h_len := hash.DIGEST_SIZES[hmac_hash]
 
 	// 1. If dkLen > (2^32 - 1) * hLen, output "derived key too long"