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Diffstat (limited to 'internal/stupidgcm/chacha.c')
-rw-r--r--internal/stupidgcm/chacha.c120
1 files changed, 102 insertions, 18 deletions
diff --git a/internal/stupidgcm/chacha.c b/internal/stupidgcm/chacha.c
index e188bfc..05d68af 100644
--- a/internal/stupidgcm/chacha.c
+++ b/internal/stupidgcm/chacha.c
@@ -9,6 +9,21 @@ static void panic(const char* const msg)
__builtin_trap();
}
+static const EVP_CIPHER* getEvpCipher(enum aeadType cipherId)
+{
+ switch (cipherId) {
+ case aeadTypeChacha:
+ return EVP_chacha20_poly1305();
+ case aeadTypeGcm:
+ return EVP_aes_256_gcm();
+ }
+ panic("unknown cipherId");
+ return NULL;
+}
+
+// We only support 16-byte tags
+static const int supportedTagLen = 16;
+
// https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption#Authenticated_Encryption_using_GCM_mode
int aead_seal(
const enum aeadType cipherId,
@@ -23,19 +38,9 @@ int aead_seal(
unsigned char* const ciphertext,
const int ciphertextBufLen)
{
- const EVP_CIPHER* evpCipher = NULL;
- switch (cipherId) {
- case aeadTypeChacha:
- evpCipher = EVP_chacha20_poly1305();
- break;
- case aeadTypeGcm:
- evpCipher = EVP_aes_256_gcm();
- break;
- default:
- panic("unknown cipherId");
- }
+ const EVP_CIPHER* evpCipher = getEvpCipher(cipherId);
- // Create scratch space "context"
+ // Create scratch space "ctx"
EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
if (!ctx) {
panic("EVP_CIPHER_CTX_new failed");
@@ -91,20 +96,99 @@ int aead_seal(
panic("EVP_EncryptFinal_ex: unexpected length");
}
- // We only support 16-byte tags
- const int tagLen = 16;
-
// Get MAC tag and append it to the ciphertext
- if (ciphertextLen + tagLen > ciphertextBufLen) {
+ if (ciphertextLen + supportedTagLen > ciphertextBufLen) {
panic("tag overflows output buffer");
}
- if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, tagLen, ciphertext + plaintextLen) != 1) {
+ if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, supportedTagLen, ciphertext + plaintextLen) != 1) {
panic("EVP_CTRL_AEAD_GET_TAG failed");
}
- ciphertextLen += tagLen;
+ ciphertextLen += supportedTagLen;
// Free scratch space
EVP_CIPHER_CTX_free(ctx);
return ciphertextLen;
}
+
+int aead_open(
+ const enum aeadType cipherId,
+ const unsigned char* const ciphertext,
+ const int ciphertextLen,
+ const unsigned char* const authData,
+ const int authDataLen,
+ unsigned char* const tag,
+ const int tagLen,
+ const unsigned char* const key,
+ const int keyLen,
+ const unsigned char* const iv,
+ const int ivLen,
+ unsigned char* const plaintext,
+ const int plaintextBufLen)
+{
+ const EVP_CIPHER* evpCipher = getEvpCipher(cipherId);
+
+ // Create scratch space "ctx"
+ EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
+ if (!ctx) {
+ panic("EVP_CIPHER_CTX_new failed");
+ }
+
+ // Set cipher
+ if (EVP_DecryptInit_ex(ctx, evpCipher, NULL, NULL, NULL) != 1) {
+ panic("EVP_DecryptInit_ex set cipher failed");
+ }
+
+ // Check keyLen by trying to set it (fails if keyLen != 32)
+ if (EVP_CIPHER_CTX_set_key_length(ctx, keyLen) != 1) {
+ panic("keyLen mismatch");
+ }
+
+ // Set IV length so we do not depend on the default
+ if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN, ivLen, NULL) != 1) {
+ panic("EVP_CTRL_AEAD_SET_IVLEN failed");
+ }
+
+ // Set key and IV
+ if (EVP_DecryptInit_ex(ctx, NULL, NULL, key, iv) != 1) {
+ panic("EVP_DecryptInit_ex set key & iv failed");
+ }
+
+ // Provide authentication data
+ int outLen = 0;
+ if (EVP_DecryptUpdate(ctx, NULL, &outLen, authData, authDataLen) != 1) {
+ panic("EVP_DecryptUpdate authData failed");
+ }
+ if (outLen != authDataLen) {
+ panic("EVP_DecryptUpdate authData: unexpected length");
+ }
+
+ // Decrypt "ciphertext" into "plaintext"
+ if (ciphertextLen > plaintextBufLen) {
+ panic("ciphertextLen overflows output buffer");
+ }
+ if (EVP_DecryptUpdate(ctx, plaintext, &outLen, ciphertext, ciphertextLen) != 1) {
+ panic("EVP_DecryptUpdate failed");
+ }
+ int plaintextLen = outLen;
+
+ // Check tag
+ if (tagLen != supportedTagLen) {
+ panic("unsupported tag length");
+ }
+ if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, tagLen, tag) != 1) {
+ panic("EVP_CTRL_AEAD_SET_TAG failed");
+ }
+ if (EVP_DecryptFinal_ex(ctx, plaintext + plaintextLen, &outLen) != 1) {
+ // authentication failed
+ return -1;
+ }
+ if (outLen != 0) {
+ panic("EVP_EncryptFinal_ex: unexpected length");
+ }
+
+ /* Clean up */
+ EVP_CIPHER_CTX_free(ctx);
+
+ return plaintextLen;
+}