[openssl-users] Optimized way to encrypt data with different ivs using AES/GCM

[me via openssl-users]

Hello OpenSSL experts,

I am encrypting a stream of data using OpenSSL C API and AES/GCM with 
16-byte ivs. The stream is split into several chunks that need to be 
encrypted with the same key but different ivs. So far I have the 
following flow:

###
for data_chunk:
    iv = newIv()
    EVP_CIPHER_CTX_new
    EVP_EncryptInit_ex(ctx, EVP_aes_128_gcm(), NULL, NULL, NULL)
    EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))
    EVP_EncryptInit_ex(ctx, NULL, NULL, key, iv))

    EVP_EncryptUpdate
    EVP_EncryptFinal_ex
    EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG...

    EVP_CIPHER_CTX_free
###

I am looking into improving performance by reusing objects, ideally the 
following way:

###
EVP_CIPHER_CTX_new
EVP_EncryptInit_ex(ctx, EVP_aes_128_gcm(), NULL, NULL, NULL)
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))

for data_chunk:
    iv = newIv()
    EVP_EncryptInit_ex(ctx, NULL, NULL, key, iv))

    EVP_EncryptUpdate
    EVP_EncryptFinal_ex
    EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG...

EVP_CIPHER_CTX_free
###

The OpenSSL documentation is not entirely clear if this is recommended, 
is there any concern with the approach? Would that also work for decryption?

Many thanks.
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