From: Nick Mathewson <nickm@torproject.org>
Date: Sun, 20 Apr 2025 22:49:40 +0000 (-0400)
Subject: aes: Support for replacing an AES key without free+alloc
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=83b9f63b860efab0473bcfa41c8c12912af2aeca;p=thirdparty%2Ftor.git

aes: Support for replacing an AES key without free+alloc
---

diff --git a/src/lib/crypt_ops/aes.h b/src/lib/crypt_ops/aes.h
index f9e95ccd0d..d6844d9b9d 100644
--- a/src/lib/crypt_ops/aes.h
+++ b/src/lib/crypt_ops/aes.h
@@ -33,6 +33,8 @@ int evaluate_ctr_for_aes(void);
 typedef struct aes_raw_t aes_raw_t;
 
 aes_raw_t *aes_raw_new(const uint8_t *key, int key_bits, bool encrypt);
+void aes_raw_set_key(aes_raw_t **cipher, const uint8_t *key,
+                     int key_bits, bool encrypt);
 void aes_raw_free_(aes_raw_t *cipher);
 #define aes_raw_free(cipher) \
   FREE_AND_NULL(aes_raw_t, aes_raw_free_, (cipher))
diff --git a/src/lib/crypt_ops/aes_nss.c b/src/lib/crypt_ops/aes_nss.c
index 55ac5a2edf..f2550e91c1 100644
--- a/src/lib/crypt_ops/aes_nss.c
+++ b/src/lib/crypt_ops/aes_nss.c
@@ -162,6 +162,15 @@ aes_raw_free_(aes_raw_t *cipher_)
   PK11_DestroyContext(ctx, PR_TRUE);
 }
 void
+aes_raw_set_key(aes_raw_t **cipher, const uint8_t *key,
+                int key_bits, bool encrypt)
+{
+  // For NSS, I could not find a method to change the key
+  // of an existing context.
+  aes_raw_free(*cipher);
+  *cipher = aes_raw_new(key, key_bits, encrypt);
+}
+void
 aes_raw_encrypt(const aes_raw_t *cipher, uint8_t *block)
 {
   SECStatus s;
diff --git a/src/lib/crypt_ops/aes_openssl.c b/src/lib/crypt_ops/aes_openssl.c
index f28b9211c2..7a03024440 100644
--- a/src/lib/crypt_ops/aes_openssl.c
+++ b/src/lib/crypt_ops/aes_openssl.c
@@ -421,6 +421,30 @@ aes_raw_new(const uint8_t *key, int key_bits, bool encrypt)
   EVP_CIPHER_CTX_set_padding(cipher, 0);
   return (aes_raw_t *)cipher;
 }
+/**
+ * Replace the key on an existing aes_raw_t.
+ *
+ * This may be faster than freeing and reallocating.
+ */
+void
+aes_raw_set_key(aes_raw_t **cipher_, const uint8_t *key,
+                int key_bits, bool encrypt)
+{
+  const EVP_CIPHER *c = *(EVP_CIPHER**) cipher_;
+  switch (key_bits) {
+    case 128: c = EVP_aes_128_ecb(); break;
+    case 192: c = EVP_aes_192_ecb(); break;
+    case 256: c = EVP_aes_256_ecb(); break;
+    default: tor_assert_unreached();
+  }
+  aes_raw_t *cipherp = *cipher_;
+  EVP_CIPHER_CTX *cipher = (EVP_CIPHER_CTX *)cipherp;
+  EVP_CIPHER_CTX_reset(cipher);
+  int r = EVP_CipherInit(cipher, c, key, NULL, encrypt);
+  tor_assert(r == 1);
+  EVP_CIPHER_CTX_set_padding(cipher, 0);
+}
+
 /**
  * Release storage held by 'cipher'.
  */