(Tcl) Understanding a few ECDSA Public Key Formats

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Describes a few ECDSA public key formats.

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load ./chilkat.dll

# Here we have the output of the following openssl command:  openssl ec -in key.pem -pubout -text

# Private-Key: (256 bit)
# priv:
#     0e:63:25:8a:73:3c:71:b6:c0:e7:a3:0f:94:b9:74:
#     e0:be:bd:46:18:be:40:7e:66:9e:21:99:85:0e:ed:
#     87:2d
# pub:
#     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
#     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
#     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
#     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
#     12:b7:b8:6a:43
# ASN1 OID: prime256v1
# NIST CURVE: P-256
# writing EC key
# -----BEGIN PUBLIC KEY-----
# MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
# Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
# -----END PUBLIC KEY-----

# The public key is shown in two different formats.
# The first is this:

# pub:
#     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
#     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
#     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
#     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
#     12:b7:b8:6a:43

# It is the ANSI X9.63 format.
# 65-bytes are the uncompressed public key (04 || X || Y) 

# This is the same public key, but in PEM format

# -----BEGIN PUBLIC KEY-----
# MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
# Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
# -----END PUBLIC KEY-----

# It contains ASN.1 that more explicitly identifies the key type.
# 
# SEQUENCE (2 elem)
#   SEQUENCE (2 elem)
#     OBJECT IDENTIFIER 1.2.840.10045.2.1 ecPublicKey (ANSI X9.62 public key type)
#     OBJECT IDENTIFIER 1.2.840.10045.3.1.7 prime256v1 (ANSI X9.62 named elliptic curve)
#   BIT STRING (520 bit) 000001000101110100011010010011111101100110111101010010011001111011100...

# PEM format can be loaded into a Chilkat public key object like this:

set sbPem [new_CkStringBuilder]

CkStringBuilder_Append $sbPem "-----BEGIN PUBLIC KEY-----\r\n"
CkStringBuilder_Append $sbPem "MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET\r\n"
CkStringBuilder_Append $sbPem "Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==\r\n"
CkStringBuilder_Append $sbPem "-----END PUBLIC KEY-----\r\n"

set pubKey1 [new_CkPublicKey]

set success [CkPublicKey_LoadFromString $pubKey1 [CkStringBuilder_getAsString $sbPem]]
if {$success == 0} then {
    puts [CkPublicKey_lastErrorText $pubKey1]
    delete_CkStringBuilder $sbPem
    delete_CkPublicKey $pubKey1
    exit
}

# The X9.63 format can be loaded like this:
set sbHex [new_CkStringBuilder]

CkStringBuilder_Append $sbHex "04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:"
CkStringBuilder_Append $sbHex "b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:"
CkStringBuilder_Append $sbHex "39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:"
CkStringBuilder_Append $sbHex "2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:"
CkStringBuilder_Append $sbHex "12:b7:b8:6a:43"

# Get rid of the ":" chars.
set numReplaced [CkStringBuilder_Replace $sbHex ":" ""]

# We'll need to convert hex to base64..
set bdKey [new_CkBinData]

CkBinData_AppendEncoded $bdKey [CkStringBuilder_getAsString $sbHex] "hex"

set pubKey2 [new_CkPublicKey]

set success [CkPublicKey_LoadFromString $pubKey2 [CkBinData_getEncoded $bdKey "base64"]]
if {$success == 0} then {
    puts [CkPublicKey_lastErrorText $pubKey2]
    delete_CkStringBuilder $sbPem
    delete_CkPublicKey $pubKey1
    delete_CkStringBuilder $sbHex
    delete_CkBinData $bdKey
    delete_CkPublicKey $pubKey2
    exit
}

# Let's get the key in pubKey2 as PEM.
# It should be idential to the PEM above.
puts [CkPublicKey_getPem $pubKey2 1]

# Here's the output.  You can see it's the same as the PEM above..

# -----BEGIN PUBLIC KEY-----
# MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
# Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
# -----END PUBLIC KEY-----

delete_CkStringBuilder $sbPem
delete_CkPublicKey $pubKey1
delete_CkStringBuilder $sbHex
delete_CkBinData $bdKey
delete_CkPublicKey $pubKey2