crypto: Enable AES-GCM tag length to change

This commit enables AES-GCM encryption/decryption to change its tag
length between 1 to 16 bytes.

3 files changed, 16 insertions, 7 deletions

diff --git a/lib/crypto/c_src/crypto.c b/lib/crypto/c_src/crypto.c
index d1f620d892..e77bbe184b 100644
--- a/lib/crypto/c_src/crypto.c
+++ b/lib/crypto/c_src/crypto.c
@@ -314,7 +314,7 @@ static ErlNifFunc nif_funcs[] = {
 
     {"rand_seed_nif", 1, rand_seed_nif},
 
-    {"aes_gcm_encrypt", 4, aes_gcm_encrypt},
+    {"aes_gcm_encrypt", 5, aes_gcm_encrypt},
     {"aes_gcm_decrypt", 5, aes_gcm_decrypt},
 
     {"chacha20_poly1305_encrypt", 4, chacha20_poly1305_encrypt},
@@ -1629,6 +1629,7 @@ static ERL_NIF_TERM aes_gcm_encrypt(ErlNifEnv* env, int argc, const ERL_NIF_TERM
     EVP_CIPHER_CTX ctx;
     const EVP_CIPHER *cipher = NULL;
     ErlNifBinary key, iv, aad, in;
+    unsigned int tag_len;
     unsigned char *outp, *tagp;
     ERL_NIF_TERM out, out_tag;
     int len;
@@ -1637,7 +1638,8 @@ static ERL_NIF_TERM aes_gcm_encrypt(ErlNifEnv* env, int argc, const ERL_NIF_TERM
 	|| (key.size != 16 && key.size != 24 && key.size != 32)
 	|| !enif_inspect_binary(env, argv[1], &iv) || iv.size == 0
 	|| !enif_inspect_iolist_as_binary(env, argv[2], &aad)
-	|| !enif_inspect_iolist_as_binary(env, argv[3], &in)) {
+	|| !enif_inspect_iolist_as_binary(env, argv[3], &in)
+	|| !enif_get_uint(env, argv[4], &tag_len) || tag_len < 1 || tag_len > 16) {
 	return enif_make_badarg(env);
     }
 
@@ -1669,9 +1671,9 @@ static ERL_NIF_TERM aes_gcm_encrypt(ErlNifEnv* env, int argc, const ERL_NIF_TERM
     if (EVP_EncryptFinal_ex(&ctx, outp+len, &len) != 1)
         goto out_err;
 
-    tagp = enif_make_new_binary(env, EVP_GCM_TLS_TAG_LEN, &out_tag);
+    tagp = enif_make_new_binary(env, tag_len, &out_tag);
 
-    if (EVP_CIPHER_CTX_ctrl(&ctx, EVP_CTRL_GCM_GET_TAG, EVP_GCM_TLS_TAG_LEN, tagp) != 1)
+    if (EVP_CIPHER_CTX_ctrl(&ctx, EVP_CTRL_GCM_GET_TAG, tag_len, tagp) != 1)
         goto out_err;
 
     EVP_CIPHER_CTX_cleanup(&ctx);
@@ -1704,7 +1706,7 @@ static ERL_NIF_TERM aes_gcm_decrypt(ErlNifEnv* env, int argc, const ERL_NIF_TERM
 	|| !enif_inspect_binary(env, argv[1], &iv) || iv.size == 0
 	|| !enif_inspect_iolist_as_binary(env, argv[2], &aad)
 	|| !enif_inspect_iolist_as_binary(env, argv[3], &in)
-	|| !enif_inspect_iolist_as_binary(env, argv[4], &tag) || tag.size != EVP_GCM_TLS_TAG_LEN) {
+	|| !enif_inspect_iolist_as_binary(env, argv[4], &tag)) {
 	return enif_make_badarg(env);
     }
 
@@ -1730,7 +1732,7 @@ static ERL_NIF_TERM aes_gcm_decrypt(ErlNifEnv* env, int argc, const ERL_NIF_TERM
 
     if (EVP_DecryptUpdate(&ctx, outp, &len, in.data, in.size) != 1)
         goto out_err;
-    if (EVP_CIPHER_CTX_ctrl(&ctx, EVP_CTRL_GCM_SET_TAG, EVP_GCM_TLS_TAG_LEN, tag.data) != 1)
+    if (EVP_CIPHER_CTX_ctrl(&ctx, EVP_CTRL_GCM_SET_TAG, tag.size, tag.data) != 1)
         goto out_err;
     if (EVP_DecryptFinal_ex(&ctx, outp+len, &len) != 1)
         goto out_err;
diff --git a/lib/crypto/doc/src/crypto.xml b/lib/crypto/doc/src/crypto.xml
index d3e827b3e6..9cb9587964 100644
--- a/lib/crypto/doc/src/crypto.xml
+++ b/lib/crypto/doc/src/crypto.xml
@@ -203,6 +203,7 @@
     <func>
       <name>block_encrypt(Type, Key, Ivec, PlainText) -> CipherText</name>
       <name>block_encrypt(AeadType, Key, Ivec, {AAD, PlainText}) -> {CipherText, CipherTag}</name>
+      <name>block_encrypt(aes_gcm, Key, Ivec, {AAD, PlainText, TagLength}) -> {CipherText, CipherTag}</name>
       <fsummary>Encrypt <c>PlainText</c> according to <c>Type</c> block cipher</fsummary>
       <type>
 	<v>Type = block_cipher() </v>
@@ -210,6 +211,7 @@
 	<v>Key = block_key() </v>
         <v>PlainText = iodata() </v>
         <v>AAD = IVec = CipherText = CipherTag = binary()</v>
+        <v>TagLength = 1..16</v>
       </type>
       <desc>
         <p>Encrypt <c>PlainText</c> according to <c>Type</c> block cipher.
diff --git a/lib/crypto/src/crypto.erl b/lib/crypto/src/crypto.erl
index 3e24ff2b0a..a9dbca3caf 100644
--- a/lib/crypto/src/crypto.erl
+++ b/lib/crypto/src/crypto.erl
@@ -302,6 +302,8 @@ block_encrypt(aes_ige256, Key, Ivec, Data) ->
     aes_ige_crypt_nif(Key, Ivec, Data, true);
 block_encrypt(aes_gcm, Key, Ivec, {AAD, Data}) ->
     aes_gcm_encrypt(Key, Ivec, AAD, Data);
+block_encrypt(aes_gcm, Key, Ivec, {AAD, Data, TagLength}) ->
+    aes_gcm_encrypt(Key, Ivec, AAD, Data, TagLength);
 block_encrypt(chacha20_poly1305, Key, Ivec, {AAD, Data}) ->
     chacha20_poly1305_encrypt(Key, Ivec, AAD, Data).
 
@@ -917,7 +919,10 @@ aes_cfb_128_decrypt(Key, IVec, Data) ->
 %%
 %% AES - in Galois/Counter Mode (GCM)
 %%
-aes_gcm_encrypt(_Key, _Ivec, _AAD, _In) -> ?nif_stub.
+%% The default tag length is EVP_GCM_TLS_TAG_LEN(16),
+aes_gcm_encrypt(Key, Ivec, AAD, In) ->
+    aes_gcm_encrypt(Key, Ivec, AAD, In, 16).
+aes_gcm_encrypt(_Key, _Ivec, _AAD, _In, _TagLength) -> ?nif_stub.
 aes_gcm_decrypt(_Key, _Ivec, _AAD, _In, _Tag) -> ?nif_stub.
 
 %%