ECC_PublicKeyFromPrivate

CryptoSys PKI Pro Manual

ECC_PublicKeyFromPrivate

Converts an internal EC private key string into an internal EC public key string.

VBA/VB6 Syntax


Public Declare Function ECC_PublicKeyFromPrivate Lib "diCrPKI.dll" (ByVal strOutput As String, ByVal nOutChars As Long, ByVal strIntKeyString As String, ByVal nOptions As Long) As Long

nRet = ECC_PublicKeyFromPrivate(strOutput, nOutChars, strIntKeyString, nOptions)

C/C++ Syntax


long __stdcall ECC_PublicKeyFromPrivate(char *szOutput, long nOutChars, const char *szIntKeyString, long nOptions);

Parameters

szOutput: [out] string of sufficient length to receive the output.
nOutChars: [in] specifying the maximum number of characters to be received.
szIntKeyString: [in] containing the private key as an internal key string.
nOptions: [in] not used in this release. Specify zero.

Returns (VBA/C)

If successful, the return value is the number of characters in or required for the output string; otherwise it returns a nonzero error code.

VBA Wrapper Syntax

Public Function eccPublicKeyFromPrivate (szIntKeyString As String, Optional nOptions As Long = 0) As String

.NET Equivalent

Ecc.PublicKeyFromPrivate Method

C++ (STL) Equivalent

static std::string dipki::Ecc::PublicKeyFromPrivate (std::string internalKey)

Python Equivalent

static Ecc.publickey_from_private(intkeystr)

Remarks

For the "raw" VBA/C function, the user must allocate an output string buffer szOutput of the required length. Specify a zero nOutChars or an empty string for szOutput to find the required length. ANSI C users must add one to this value when allocating memory.

Use this to derive the public key from the EC private key, where both values are represented as "internal" key strings.

Example (VBA core function)

Dim nRet As Long
Dim nChars As Long
Dim strIntPriKey As String
Dim strIntPubKey As String
Dim strKeyFile As String
Dim strNewKeyFile As String
Dim strPassword As String
Dim strTypeName As String
Dim strFileName As String

strKeyFile = "myeckeyp521.p8"
strPassword = "password"

' 1. READ IN THE PRIVATE KEY: int_string <- file
Debug.Print "FILE: " & strKeyFile
' Find required length of internal key string
nChars = ECC_ReadPrivateKey("", 0, strKeyFile, strPassword, 0)
Debug.Print "ECC_ReadPrivateKey returns " & nChars & " (expected +ve)"
If (nChars <= 0) Then Exit Sub   ' CATCH ERROR HERE
' Dimension the string to receive output
strIntPriKey = String(nChars, " ")
' Read into internal key string
nChars = ECC_ReadPrivateKey(strIntPriKey, Len(strIntPriKey), strKeyFile, strPassword, 0)
Debug.Print "[" & strIntPriKey & "]"

' 2. CONVERT TO PUBLIC: int_string <-- int_string
nChars = ECC_PublicKeyFromPrivate("", 0, strIntPriKey, 0)
Debug.Print "ECC_PublicKeyFromPrivate returns " & nChars & " (expected +ve)"
If (nChars <= 0) Then Exit Sub   ' CATCH ERROR HERE
strIntPubKey = String(nChars, " ")
nChars = ECC_PublicKeyFromPrivate(strIntPubKey, Len(strIntPubKey), strIntPriKey, 0)
Debug.Print "[" & strIntPubKey & "]"
      
' 3. SAVE AS NEW PUBLIC KEY FILE: file <-- int_string
strNewKeyFile = "myeckeyp521_new.pub"
nRet = ECC_SaveKey(strNewKeyFile, strIntPubKey, 0)
Debug.Print "ECC_SaveKey returns " & nRet & " (expected 0)"

' Check the type of file we made
strTypeName = String(PKI_ASN1_TYPE_MAXCHARS, " ")
strFileName = strNewKeyFile
nChars = ASN1_Type(strTypeName, Len(strTypeName), strFileName, 0)
If nChars > 0 Then Debug.Print strFileName & ": " & Left(strTypeName, nChars)

FILE: myeckeyp521.p8
ECC_ReadPrivateKey returns 336 (expected +ve)
[PVECRDe...PmEAIGm5Uj1HI=]
ECC_PublicKeyFromPrivate returns 212 (expected +ve)
[MIGbMBA...sxHXznms=]
ECC_SaveKey returns 0 (expected 0)
myeckeyp521_new.pub: PUBLIC KEY INFO

Example (VBA wrapper function)

Dim strIntKey As String

' Read in public key from file
strIntKey = eccReadPublicKey("myeckeyp256.pub")
Debug.Assert Len(strIntKey) > 0
Debug.Print "Key curve=" & eccQueryKey(strIntKey, "curveName", 0) & " keyBits=" & _
    eccQueryKey(strIntKey, "keyBits", 0) & _
    " and is a " & _
    IIf(eccQueryKey(strIntKey, "isPrivate") = "1", "Private", "Public") & " key"
Debug.Print eccQueryKey(strIntKey, "publicKey")
Debug.Print "KeyHashCode=0x" & Hex(ECC_KeyHashCode(strIntKey))

' Read in private key from file
strIntKey = eccReadPrivateKey("myeckeyp256.p8", "password")
Debug.Assert Len(strIntKey) > 0
Debug.Print "Key curve=" & eccQueryKey(strIntKey, "curveName", 0) & " keyBits=" & _
    eccQueryKey(strIntKey, "keyBits", 0) & _
    " and is a " & _
    IIf(eccQueryKey(strIntKey, "isPrivate") = "1", "Private", "Public") & " key"
Debug.Print eccQueryKey(strIntKey, "publicKey")
Debug.Print "KeyHashCode=0x" & Hex(ECC_KeyHashCode(strIntKey))

' Derive public key from private key
strIntKey = eccPublicKeyFromPrivate(strIntKey)
Debug.Assert Len(strIntKey) > 0
Debug.Print "Key curve=" & eccQueryKey(strIntKey, "curveName", 0) & " keyBits=" & _
    eccQueryKey(strIntKey, "keyBits", 0) & _
    " and is a " & _
    IIf(eccQueryKey(strIntKey, "isPrivate") = "1", "Private", "Public") & " key"
Debug.Print eccQueryKey(strIntKey, "publicKey")
Debug.Print "KeyHashCode=0x" & Hex(ECC_KeyHashCode(strIntKey))