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fixed size of IV size of 16Byte for AES-CBC #112

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fixed size of IV size of 16Byte for AES-CBC #112

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32 changes: 17 additions & 15 deletions src/jwe.c
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Original file line number Diff line number Diff line change
Expand Up @@ -871,23 +871,25 @@ static bool _cjose_jwe_set_iv_aes_cbc(cjose_jwe_t *jwe, cjose_err *err)
CJOSE_ERROR(err, CJOSE_ERR_INVALID_ARG);
return false;
}
const char *enc = json_string_value(enc_obj);

cjose_get_dealloc()(jwe->enc_iv.raw);
jwe->enc_iv.raw_len = 0;

if (strcmp(enc, CJOSE_HDR_ENC_A128CBC_HS256) == 0)
jwe->enc_iv.raw_len = 16;
if (strcmp(enc, CJOSE_HDR_ENC_A192CBC_HS384) == 0)
jwe->enc_iv.raw_len = 24;
if (strcmp(enc, CJOSE_HDR_ENC_A256CBC_HS512) == 0)
jwe->enc_iv.raw_len = 32;

if (jwe->enc_iv.raw_len == 0)
{
CJOSE_ERROR(err, CJOSE_ERR_INVALID_ARG);
return false;
}
// RFC 7516 (https://tools.ietf.org/html/rfc7516) is unclear about
// the size of the IV for AES-CBC. In section 5.1
// (https://tools.ietf.org/html/rfc7516#section-5.1), they state in no. 9.:
// "Generate a random JWE Initialization Vector of the correct size
// for the content encryption algorithm"
// And in the example in A.2.4 (https://tools.ietf.org/html/rfc7516#appendix-A.2.4)
// they provide an example for AES128-CBC, which results (naturally) in the IV size of 128Bit.
//
// The CISCO implementation chooses for the size of the IV the key size of the
// cipher algorithm, which seems to be wrong.
//
// According to RFC 3602 section 3 (https://tools.ietf.org/html/rfc3602#section-3):
// "The IV field MUST be the same size as the block size of the cipher algorithm being used."
// And because the block size for AES cipher is always 16 Byte, the IV must be 16 Byte long.
//
// IV size for AES CBC is always 16 Byte
jwe->enc_iv.raw_len = 16;

// generate IV as random iv_size * 8 bit value
if (!_cjose_jwe_malloc(jwe->enc_iv.raw_len, true, &jwe->enc_iv.raw, err))
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