Visual FoxPro

MIME S/MIME Signing Algorithm Properties

Demonstrates the properties that control S/MIME signing: SigningAlg (the RSA signature scheme, PKCS1-V1_5 or RSASSA-PSS), SigningHashAlg (the message-digest algorithm), Micalg and Protocol (the micalg and protocol parameters of a multipart/signed Content-Type), and UseXPkcs7 (whether historical x-pkcs7 media-type names are used). The properties are configured before creating a detached signature.

Background. These settings determine how the CMS/PKCS #7 signature is produced and how a multipart/signed wrapper advertises it. The defaults (PKCS1-V1_5, sha256) suit most modern uses; the properties allow interoperability with specific requirements.

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LOCAL lnSuccess
LOCAL loMime
LOCAL lcPfxPassword
LOCAL loCert

lnSuccess = 0

loMime = CreateObject('Chilkat.Mime')
lnSuccess = loMime.SetBodyFromPlainText("This message will be signed.")
IF (lnSuccess = 0) THEN
    ? loMime.LastErrorText
    RELEASE loMime
    CANCEL
ENDIF

*  SigningAlg is the RSA signature scheme.  The default is PKCS1-V1_5; set RSASSA-PSS (or pss) for
*  RSASSA-PSS.
loMime.SigningAlg = "PKCS1-V1_5"

*  SigningHashAlg is the message-digest algorithm.  The default is sha256.
loMime.SigningHashAlg = "sha256"

*  Micalg and Protocol are the micalg and protocol parameters written into a multipart/signed
*  Content-Type header field.  They are normally set automatically, but can be controlled here.
loMime.Micalg = "sha-256"
loMime.Protocol = "application/pkcs7-signature"

*  UseXPkcs7 controls whether newly created S/MIME media types use the historical x-pkcs7 names.
loMime.UseXPkcs7 = 0

*  Load a signing certificate (with private key access) from a PFX.  The PFX password should come
*  from a secure source rather than being hard-coded.
lcPfxPassword = "myPfxPassword"
loCert = CreateObject('Chilkat.Cert')
lnSuccess = loCert.LoadPfxFile("qa_data/signer.pfx",lcPfxPassword)
IF (lnSuccess = 0) THEN
    ? loCert.LastErrorText
    RELEASE loMime
    RELEASE loCert
    CANCEL
ENDIF

*  Create the detached signature using the algorithms configured above.
lnSuccess = loMime.AddDetachedSignature(loCert)
IF (lnSuccess = 0) THEN
    ? loMime.LastErrorText
    RELEASE loMime
    RELEASE loCert
    CANCEL
ENDIF

? "Signed with SigningAlg=" + loMime.SigningAlg + " SigningHashAlg=" + loMime.SigningHashAlg

RELEASE loMime
RELEASE loCert