libtpmtss: Read RSA public key exponent instead of assuming its value

Up to now it was assumed that the RSA public key exponent is equal to 2^16+1.
Although this is probably true in most if not all cases, it is not correct
according to the TPM 2.0 specification.

This patch fixes that by reading the exponent from the structure returned
by TPM2_ReadPublic.

Closes strongswan/strongswan#121.

diff --git a/src/libtpmtss/tpm_tss_tss2_v1.c b/src/libtpmtss/tpm_tss_tss2_v1.c
index f904442edebe2c8a0a18049a01bc1273cfa33563..1c214afa37aa723f27076876d0f0c54743485dca 100644 (file)
--- a/src/libtpmtss/tpm_tss_tss2_v1.c
+++ b/src/libtpmtss/tpm_tss_tss2_v1.c
@@ -481,6 +481,7 @@ METHOD(tpm_tss_t, get_public, chunk_t,
                        TPM2B_PUBLIC_KEY_RSA *rsa;
                        TPMT_RSA_SCHEME *scheme;
                        chunk_t aik_exponent, aik_modulus;
+                       uint32_t exponent;
 
                        scheme = &public.t.publicArea.parameters.rsaDetail.scheme;
                        sig_alg   = scheme->scheme;
@@ -488,7 +489,15 @@ METHOD(tpm_tss_t, get_public, chunk_t,
 
                        rsa = &public.t.publicArea.unique.rsa;
                        aik_modulus = chunk_create(rsa->t.buffer, rsa->t.size);
-                       aik_exponent = chunk_from_chars(0x01, 0x00, 0x01);
+                       exponent = public.t.publicArea.parameters.rsaDetail.exponent;
+                       if (!exponent)
+                       {
+                               aik_exponent = chunk_from_chars(0x01, 0x00, 0x01);
+                       }
+                       else
+                       {
+                               aik_exponent = chunk_from_thing(exponent);
+                       }
 
                        /* subjectPublicKeyInfo encoding of RSA public key */
                        if (!lib->encoding->encode(lib->encoding, PUBKEY_SPKI_ASN1_DER,

diff --git a/src/libtpmtss/tpm_tss_tss2_v2.c b/src/libtpmtss/tpm_tss_tss2_v2.c
index 6bbbce238fc4ae7bffdd25b62656ab826d87fcc8..cac0dd6617f5439931283e95c0b14da8e882f6b7 100644 (file)
--- a/src/libtpmtss/tpm_tss_tss2_v2.c
+++ b/src/libtpmtss/tpm_tss_tss2_v2.c
@@ -435,6 +435,7 @@ METHOD(tpm_tss_t, get_public, chunk_t,
                        TPM2B_PUBLIC_KEY_RSA *rsa;
                        TPMT_RSA_SCHEME *scheme;
                        chunk_t aik_exponent, aik_modulus;
+                       uint32_t exponent;
 
                        scheme = &public.publicArea.parameters.rsaDetail.scheme;
                        sig_alg   = scheme->scheme;
@@ -442,7 +443,15 @@ METHOD(tpm_tss_t, get_public, chunk_t,
 
                        rsa = &public.publicArea.unique.rsa;
                        aik_modulus = chunk_create(rsa->buffer, rsa->size);
-                       aik_exponent = chunk_from_chars(0x01, 0x00, 0x01);
+                       exponent = public.publicArea.parameters.rsaDetail.exponent;
+                       if (!exponent)
+                       {
+                               aik_exponent = chunk_from_chars(0x01, 0x00, 0x01);
+                       }
+                       else
+                       {
+                               aik_exponent = chunk_from_thing(exponent);
+                       }
 
                        /* subjectPublicKeyInfo encoding of RSA public key */
                        if (!lib->encoding->encode(lib->encoding, PUBKEY_SPKI_ASN1_DER,